73+ 


• 


AGRIC.  LIBRARY 

LIBRARY 

UNIVERSITY  OF  CALIFORNIA. 

GIF-T  OF 

r\ 
Class 


BACTERIA 


IN  THEIR 


BELATION  TO  VEGETABLE  TISSUE 


A  DISSERTATION 

PRESENTED   TO   THE   BOARD  OF  UNIVERSITY  STUDIES   OF   THE 

JOHNS   HOPKINS   UNIVERSITY   FOR  THE   DEGREE 

OF   DOCTOR  OF   PHILOSOPHY 

BY 

H.  L.  RUSSELL 

*7 

1892 


PRESS  OP 

THE  FRIEDENWALD  COMPANY 
BALTIMORE 


• 


CONTENTS. 

PAGE 

Introduction 1 

Current  views  as  to  the  exemption  of  vegetable  tissue  from  attacks  of  micro- 
organisms      2 

Methods  used  in  experimental  work 3 

Do  healthy  plant  tissues  normally  contain  bacteria  ? 4 

Results  of  artificial  inoculation  of  bacteria  into  vegetable  tissues : 

1.  With  saprophytic  species 5 

2.  With  species  parasitic  for  animals 6 

3.  With  species  parasitic  for  plants .  7 

Conclusions  derived  and  arguments  to  show  that  distribution  of  germs  in  tissue 

depends  upon  actual  growth 8 

Can  bacteria  penetrate  the  intact  healthy  membranes  of  the  plant  ? 11 

The  action  of  bacteria  within  the  tissues,  their  mode  of  transport,  etc 13 

Resistance  and  immunity  of  plants  toward  bacteria 15 

Distinction  between  normal  resistance  and  immunity  in  the  plant  organism  .    .  17 

Examples  illustrating  the  phenomena  of  resistance  and  immunity 20 

Causes  producing  this  condition 23 

Physical 24 

Chemical     26 

Do  plant  juices  possess  germicidal  properties  ? 27 

Conclusions 32 

Bibliography 34 

Appendix  giving  a  tabular  resume  of  all  the  bacterial  plant  diseases  known  to 

date  .                                                                                                                     .  35 


BACTERIA  IN  THEIR  RELATION  TO  VEGETABLE 

TISSUE. 

BY  H.  L.  RUSSELL. 

The  relations  of  that  group  of  micro-organisms  known  as  bacteria 
to  the  animal  kingdom  have  within  the  past  two  decades  been  made 
the  subject  of  unusual  attention. 

No  department  of  the  rapidly  developing  branches  of  science  has 
been  the  field  of  greater  activity,  yet,  strange  to  say,  the  relations 
which  these  organisms  bear  to  the  co-ordinate  branch  of  biology,  the 
vegetable  kingdom,  have  been  greatly  neglected. 

Botanists  have  studied  bacteria  as  a  class,  more  or  less,  in  order  to 
determine,  if  possible,  their  affinities  with  other  low  forms  of  life,  but 
the  greater  activity  in  this  field  has  been  largely  due  to  the  close 
relation  which  they  bear  to  medicine  in  the  etiology  of  disease. 

In  regard  to  the  relations  which  they  bear  to  and  the  influence  that 
they  exert  upon  higher  plant  life,  the  data  we  possess  are  meager. 
The  progress  which  has  already  been  made  in  this  department  of 
plant  pathology  comes  largely  from  this  side  of  the  Atlantic,  and  to  a 
prominent  American  botanist,  Prof.  T.  J.  Burrill,  belongs  the  honor 
of  having  been  the  first  to  work  out  the  causal  relation  between  a 
specific  microbe  and,  a  plant  malady  (pear-blight,  1878). 

Although  Prof.  BurrilPs  work  was  done  over  a  decade  ago,  com- 
paratively little  notice  has  been  taken  of  it  by  European  writers, 
with  but  few  exceptions,  and  the  majority  of  the  text-books  that  refer 
to  it  at  all  regard  the  case  as  not  thoroughly  proven  ;  but  upon  what 
grounds  these  conclusions  are  based  it  is  quite  impossible  for  one  to 
understand  who  has  had  access  to  the  already  widely  published  data. 

It  seems  to  be  a  wide-spread  belief  that  plants  do  not  suffer  to  any 
great  extent  from  the  attacks  of  these  micro-organisms.  The  reasons 
usually  assigned  for  this  so-called  immunity  are  various.  Chief 
among  them,  however,  is  that  which  bases  the  freedom  of  plants  from 
bacterial  attack  upon  the  acidity  of  the  plant-tissue.  Other  subsidi- 
ary reasons  are  also  advanced  by  various  authors. 


2  H.  L.  Russdl 

Fliigge1  states  that  bacteria  almost  never  attack  higher  plants, 
giving  as  an  only  exception  Wakker's  hyacinth-disease.  The  low 
temperature  of  plants  and  the  chemical  composition  of  vegetable 
juices  he  regards  as  very  unfavorable  for  the  development  of  bacteria, 
more  especially  as  the  cell-juices  almost  always  possess  a  distinct 
acid  reaction,  and  thus  protect  the  plant  against  these  micro- 
organisms, which  are  so  sensitive  in  this  respect. 

Hartig,in  the  recent  edition  of  his  Lehrbuch  der  Baumkrankheiten 
(p.  37),  also  urges  the  view  that  the  acid  reaction  of  plants  prevents 
the  growth  and  development  of  bacteria,  and  that  they  play  a  very 
unimportant  role  in  the  production  of  plant-disease.  In  the  hyacinth- 
disease  above  referred  to,  he  says  the  bacteria  do  not  attack  sound, 
well-ripened  bulbs  under  normal  conditions,but  only  when  the  tissues 
have  been  more  or  less  injured  by  wounds  or  previous  attacks  of  fungi. 

He  notices,  also,  BurrilPs  claim  that  the  pear-blight  is  caused  by 
a  specific  bacillus,  but  is  somewhat  skeptical  that  the  form  referred 
to  is  anything  but  a  secondary  accompaniment  of  the  malady. 

DeBary  is  inclined  to  support  the  general  views  advanced  by 
Hartig,  but  in  his  last  edition  of  Die  Bakterien  (S.  36)  he  states  that 
it  might  be  possible  for  bacteria  to  gain  access,  through  stomata,  into 
the  tissues  of  higher  plants,  but  that  this  is  probable  is  yet  undeter- 
mined and  needs  further  investigation. 

These  observers,  all  of  them  recognized  authorities  in  the  realm  of 
pathology,  seem  to  regard  it  as  quite  improbable  that  bacteria  have 
any  important  bearing  upon  the  production  of  plant-disease.  Whether 
this  unanimity  of  expression  is  due  to  the  actual  absence  of  bacterial 
plant-maladies  in  Europe  generally,  or  because  investigations  have 
not  been  directed  in  these  channels,  can  only  be  inferred. 

In  consideration  of  the  fact  that  this  branch  of  vegetable  pathology 
is  of  increasing  importance,  and  that  the  reasons  assigned  for  the 
apparent  exemption  of  plant-tissues  from  the  attacks  of  micro-organ- 
isms have  been  largely  based  upon  the  general  law  known  in  regard 
to  bacterial  life  in  general,  it  was  deemed  advisable  that  a  series  of 
investigations  should  be  carried  out  with  different  micro-organisms, 
to  see  what  effect  contact  with  the  living  plant-tissues  would  have 
upon  them;  so,  at  the  suggestion  of  Prof.  Welch,  this  topic  was  taken 
up  for  consideration. 

1  Die  Mikroorganismen,  S.  515. 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  3 

I  have  been  unable  to  find  any  literature  upon  this  particular 
question  with  the  exception  of  a  preliminary  report  by  Lominsky, 
who  worked  mainly  with  those  forms  which  are  pathogenic  for 
animals.  His  original  paper  is  in  Russian,  so  I  have  been  forced  to 
rely  solely  upon  an  abstract  (Cent,  fur  Bakt.,  Bd.  VIII,  325)  for 
his  data. 

Aside  from  this  single  exception,  I  find  no  general  series  of 
experiments  recorded  as  giving  the  effect  of  vegetable  tissues  upon 
various  forms  of  bacterial  life. 

METHOD  OF  EXPERIMENT. 

The  following  outline  will  indicate  the  manner  in  which  the 
experiments  were  carried  out.  Fresh  cultures  of  the  various  micro- 
organisms were  always  taken  (usually  bouillon  cultures  12-24  hrs. 
old),  so  as  to  insure  the  introduction  of  non-sporogenous  material. 
A  young  growing  stem  was  selected,  so  as  to  give  the  most  favorable 
conditions  for  the,  development  of  the  organism.  It  was  first  washed 
with  sterile  water  and  then  pierced  with  a  fine  sterilized  platinum 
needle.  Into  this  minute  opening  a  tiny  droplet  of  culture  fluid  was 
injected  from  a  capillary  pipette.  The  slight  puncture  caused  by 
the  penetration  of  the  needle  was  then  closed  from  the  influence  of 
air  and  possibility  of  accidental  contamination,  by  sterile  vaseline. 

The  results  were  determined  by  excising  a  section  of  the  infected 
stem,  the  surface  having  been  slightly  flamed  in  a  Bunsen  flame. 

The  cortical  layer  was  then  removed  with  a  sterile  scalpel,  leaving 
the  inner  tissue  into  which  the  organism  had  been  injected.  Quite 
thin  sections  of  this  remaining  tissue  were  cut,  under  aseptic  precau- 
tions, and  inoculated  into  tubes  of  melted  gelatine  and  roll  cultures 
made  therefrom.  As  the  fluid  gelatine  easily  penetrates  the  plant- 
tissue,  a  moderately  thin  section  may  be  examined,  under  considerable 
magnification,  with  ease.  The  tissue  was  sectioned,  not  only  at  the 
inoculation  point,  but  at  varying  distances  above  and  below.  By 
growing  these  serial  sections  in  sets  of  culture  tubes,  one  is  able  to 
determine  how  far  the  bacteria  have  spread  .throughout  the  plant. 

An  objection  to  this  method  lies  in  the  fact  that  small  variations 
in  the  germ-content  cannot  be  detected,  as  it  is  quite  impossible  to 
prepare  the  tissue  so  that  all  germs  present  can  develop ;  but  where 
cultures  made  from  tissue  taken  at  the  point  of  inoculation  reveal 


4  H.  L.  Russell. 

but  few  germs,  we  may  safely  conclude  that  they  have  either  been 
killed  off  by  the  plant  or  died  from  insufficient  nutrition. 

On  the  other  hand,  an  increase  can  only  be  considered  probable 
where  the  cultures,  not  only  from  tne  tissue  immediately  surrounding 
the  inoculation  point,  but  at  a  distance  from  it,  reveal  a  large  number 
of  germs.  Even  the  fact  that  bacteria  are  to  be  found  at  a  greater  or 
less  distance  from  point  of  introduction  does  not  necessarily  show 
that  an  actual  increase  has  taken  place.  Their  presence  at  this  point 
might  be  considered  as  due  either  to  simple  diffusion  or  to  mechani- 
cal transportation  by  the  fluids  of  the  plant.  The  effect  of  these 
possible  factors  will,  however,  be  shown  later  to  be  quite  nugatory. 

If  macroscopical  changes  are  to  be  seen  in  the  tissue,  it  would  be 
of  itself  sufficient  evidence  that  actual  multiplication  of  the  micro- 
organisms had  taken  place.  In  addition  to  culture  methods  to  deter- 
mine the  presence  or  absence  of  bacteria  in  the  infected  tissues,  sec- 
tions were  also  subjected  to  microscopical  examination. 

But  this  method  proved  quite  unsatisfactory,  except  where  the 
bacteria  in  the  tissues  were  numerous,  as  in  the  case  of  actual  infec- 
tion. The  granular  detritus  and  peculiar  rod-like  masses  of  proto- 
plasm often  found  in  matured  cells  make  it  extremely  difficult  to 
differentiate  the  bacteria  in  an  unstained  condition.  The  use  of 
staining  methods,  so  successful  in  the  differentiation  of  bacteria  in 
sections  of  animal  tissue,  have  not  as  yet  been  successfully  applied  to 
bacteria  in  plants.  The  aniline  stains,  toward  which  the  bacteria 
are  so  susceptible,  seem  to  impregnate  the  vegetable  cell  and  its 
membranes  with  great  ease,  and  in  the  use  of  decolorizing  agents, 
parts  of  the  plant  cell  retain  the  stain  as  deeply  as  do  the  bacteria. 

Before  detailing  the  results  of  the  experiments  made,  we  will  con- 
sider briefly  the  presence  of  bacteria  in  normal  uninjured  plant- 
tissues.  This,  for  a  considerable  time,  has  been  a  debatable  question, 
and  the  recorded  results  of  numerous  observers  are  somewhat  at 
variance  with  one  another.1  The  preponderance  of  evidence  is,  how- 
ever, certainly  against  the  view  that  micro-organisms  are  present 
normally  in  the  tissues  of  higher  plants,  and  this  conclusion  harmon- 
izes well  with  what  we  know  in  the  domain  of  animal  life. 

In  the  examination  of  plant-tissues  I  have  made  a  large  number 
of  cultures,  according  to  the  method  described  above,  from  plants 

1  See  bibliography,  page  34. 


Bacteria  in  their  Relation  to   Vegetable  Tissue. 


selected  as  healthy  in  all  respects,  without  being  able  to  isolate  bac- 
teria from  them.  Bacteria,  however,  were  often  found  in  tissue  which 
had  been  wounded  from  any  cause,  and  in  some  cases  in  such  num- 
bers as  to  lead  one  to  think  that  they  had  possibly  multiplied  in  the 
plant-tissue.  This  can  happen  from  the  local  death  of  the  wounded 
tissue,  which  will  enable  the  micro-organisms  to  gain  a  foothold,  and 
even  though  they  may  not  be  able  to  grow  within  the  living  plant, 
they  are  able  to  exist  for  a  considerable  length  of  time  (as  will  be  shown 
by  the  results  of  artificial  inoculation),  and  thus  come  to  be  enclosed 
in  the  plant  by  the  healing  over  of  the  wounded  tissue.  This  is,  I 
think,  a  probable  explanation  of  the  data  recorded  by  some  observers 
who  claim  to  have  actually  isolated  saprophytic  forms  from  plant- 
tissues.1  Lesions  so  slight  as  to  escape  notice,  especially  in  root 
crops,  would  allow  the  access  of  saprophytic  forms  to  the  tissues  of  the 
plant,  where  they  might  survive  for  a  considerable  length  of  time. 

From  the  results  of  my  own  experiments,  the  conclusion  seems 
evident  that,  normally,  the  healthy  plant,  with  intact  outer  membranes, 
is  free  from  bacteria  within  its  tissues. 

In  the  tabulated  results  obtained  by  the  artificial  inoculation  of 
different  bacterial  species  into  vegetable  tissue,  they  will  be  classified 
according  to  their  nutritive  adaptation. 

TABLE  SHOWING  ACTION  OF  SAPROPHYTES  IN  PLANT  TISSUE. 


Name  of  Germ. 

Date  of  In- 
oculation. 

Date  of 
Close  of 
Exp. 

Period  of 
Incuba- 
tion. 
Days. 

Host  Plant. 

Result. 

B.  prodigiosus  

X.  20 

XI.  17 

27 

Tradescantia 

#*2   *•" 

« 
« 
« 

X.  20 
XL  26 
XII.  20 
XII.  20 

II.    1 
XII.    5 
II.    2 
II.    2 

103 
10 
42 
48 

<  « 

Geranium. 

« 

« 

* 
ft* 

** 

B    lllt6US        .... 

XI.  28 
XII  20 

XII.  10 

I  28 

13 

40 

Lima  Bean. 
Geranium 

* 
** 

B  megaterium  .                . 

XI  19 

XI  30 

11 

Lima  Bean 

* 

« 
B  coli  commune  

XI.  19 
1.12 
XII     1 

XI.  30 
11.25 
XII  20 

11 
44 
19 

it 

Geranium. 

jt 
** 

«        '  <« 

XII.    1 
I  12 

XII.  30 
II  16 

29 
35 

## 

•* 

1.  12 

II  24 

43 

** 

B  Icictis  aerogenes 

I     4 

U14 

'10 

• 

1  Fazio  and  others  :  Revista  Internaz.  d'Igiene,  (1890),  I,  3. 

2  Explanation  of  signs  :  *  denotes  presence  in  moderate  numbers. 

**      "  "  "  large  " 

—       "       absence  in  culture  entirely. 


6  H.  L.  Russell. 

The  above  table  indicates  that  a  number  of  different  forms  which 
are  ordinarily  saprophytic  in  their  method  of  nutrition,  are  able  to 
exist  within  the  plant  for  a  considerable  period  of  time,  and  in  some 
cases  show  evidence  of  a  considerable  increase.  This  multiplication 
does  not,  however,  reach  a  stage  macroscopically  observable.  There 
is  usually  a  slight  "browning"  or  discoloration  of  the  tissue  at  the 
seat  of  inoculation,  but  this  is  due  to  the  slight  injury  caused  by  the 
inoculating  needle,  even  though  the  opening  is  protected  from  the 
influence  of  the  air  by  vaseline. 

The  results  which  were  obtained  by  Lominsky1  in  regard  to  the 
growth  of  Bac.  prodigiosus  I  was  unable  to  confirm.  He  states  that 
this  germ,  inoculated  into  the  leaves  of  certain  plants,  produced 
brick-red  spots  and  stripes  which  were  to  be  seen  by  the  naked  eye. 
In  the  above  experiment  bacteria  were  demonstrated  as  present  in 
large  numbers  in  tissue  even  after  a  considerable  lapse  of  time, 
but  no  signs  could  be  detected  of  a  change  in  the  cellular  structure 
in  any  case. 

In  regard  to  forms  which  are  naturally  pathogenic  for  animals,  we 
might  expect  a  priori  that  they  would  be  unable  to  survive  for  such 
a  length  of  time,  or  show  as  marked  an  increase,  as  saprophytic  forms, 
which  are,  as  a  rule,  less  sensitive  in  regard  to  the  substratum  for 
their  development.  This  expectation  was  realized,  as  will  be  seen 
from  the  subjoined  table,  which  comprises  those  forms  that  are 
natural  facultative  parasites  on  animals. 

In  this  group  of  parasites  I  find,  with  but  few  exceptions,  that 
they  are  unable  to  compete  with  the  unfavorable  environment  to 
which  they  are  subjected  in  the  plant.  The  large  majority  of  them 
are  not  able  even  to  hold  their  own,  but  gradually  succumb  to  their 
unfavorable  surroundings.  Here  again  I  failed  to  verify  some  of 
the  results  obtained  by  Lominsky.  His  experiments  were  confined 
to  the  action  of  plant-tissues  upon  anthrax,  the  typhoid  bacillus,  and 
Staph.  pyog.  aureus.  He  made  quite  a  number  of  experiments,  and 
found  that  both  the  anthrax  and  the  pyogenic  organism  increased  and 
were  able  to  form  colonies  in  the  tissues.  Anthrax  grew  rapidly 
for  a  time,  formed  spores,  and  finally  seemed  to  undergo  degen- 
eration. The  typhoid-fever  bacillus  was  unable,  however,  to  live 
beyond  a  few  days,  and  even  then  showed  degenerating  peculiarities. 

1  Loc.  cit. 


Bacteria  in  their  Relation  to   Vegetable  Tissue. 

\*£A>.  /t:->ow\x 

TABLE  SHOWING  ACTION  OF  ANIMAL  PABASITIC  FORMS  IN 
VEGETABLE  TISSUE. 


Name  of  Germ. 

Date  of  In- 
oculation. 

End  of 
Experi- 
ment. 

Period  of 
Incuba- 
tion. 
Days. 

Host  Plant. 

Result. 

B   pyocyaneus  

XL  27 

II.    4 

69 

Begonia,  cult 

** 

« 

c  t 

B.  anthracis  

XL  28 
XL  27 
XL  20 

XII.  30 
I.    2 
I.  26 

32 
36 

38 

Geranium. 
Penthorum. 
Geranium. 

**  *-<^ 

-X-* 

<  * 
Staph.  epid.  alb  

XL  19 
XL  20 
XI  20 

XL  30 
XL  25 

I.  28 

11 
5 
40 

Lima  Bean. 
Echino  cactus. 
Geranium. 

(6)1 
(2) 

Staph.  pyog.  aureus. 

«          a,          (( 

Mic  C6reus  flav 

I.  12 
XII.  10 
I   12 

11.23 
XII.  23 
II  19 

42 
13 

38 

ft 

Lima  Bean. 
Geranium 

(3) 
(4) 

Cholera  gallinarum.  . 
Schweineseuche 

II.  20 
III     8 

III.  10 
III  25 

18 
17 

(i 

y' 

** 

Mic  tetragenus 

III  22 

IV   16 

25 

« 

Bac    diphtherisB 

III     8 

III   18 

10 

14 

1  Numbers  in  parenthesis  indicate  number  of  colonies  found  in  culture  made  from 
infected  tissue. 

It  is  noteworthy  in  the  above  table  that  the  pyogenic  organisms 
in  general  do  not  seem  to  be  especially  resistant.  With  the  single 
exception  of  the  blue  pus-germ,  they  succumbed  to  the  unfavorable 
influence  of  the  plant-tissues. 

The  consideration  of  the  third  class,  that  of  bacterial  plant  para- 
sites, brings  us  to  those  forms  which  are,  in  a  restricted  sense  at  least, 
the  natural  enemies,  of  vegetable  life. 

I  have  found  it  impossible  to  obtain  cultures  of  more  than  a  few 
of  the  germs  which  have  been  reported  as  having  been  isolated  in  the 
various  plant-maladies,  as  in  many  cases  cultures  are  not  kept  in 
stock,  even  by  the  discoverers  of  the  germ. 

Of  those  secured  I  made  a  series  of  infection  experiments  in  a 
number  of  different  hosts,  to  ascertain  the  effect  of  vegetable  tissues 
in  other  than  their  natural  hosts. 

The  pear-blight  germ  grown  in  a  Begonia-plant  for  30  days  showed 
at  end  of  that  time  large  numbers  at  inoculation  point,  but  not  dis- 
tributed throughout  the  plant.  The  same  result  was  found  when 
injected  into  Phaseolus  vulgar  is  for  30  days,  also  in  Ph.  lunatus  for 
16  days.  In  Tradescantia  alba,  no  trace  could  be  found  at  the  end 
of  60  days'  incubation  in  this  tissue.  Bac.  avense  was  injected  into 
tissue  of  Begonia,  onion,  corn,  wheat,  and  squash,  but  in  no  case 


H.  L.  Russell. 


was  any  pathological  change  macroscopically  observable.  The 
bacilli  were  not  killed  out  in  the  plant-tissue,  however,  as  they  were 
isolated  from  Begonia  and  squash  in  large  numbers,  after  30  days7 
incubation  in  these  tissues,  but  their  presence  was  confined  to  the 
tissue  contiguous  to  point  of  introduction. 

The  results  of  the  foregoing  inoculation  experiments  made  with 
various  forms  of  micro-organisms,  saprophytes  as  well  as  parasites 
(both  for  animals  and  vegetables),  show  that  these  germs  in  many 
cases  are  able  to  live  in  the  plant-tissues  for  a  considerable  length  of 
time.  A  number  of  the  different  forms,  particularly  saprophytes, 
are  able  to  grow  and  spread  throughout  the  plant  to  a  limited 
extent.  Of  the  parasitic  species  tested,  very  few  showed  any  ten- 
dency to  thus  spread.  Even  those  forms  that  are  natural  parasites 
of  certain  higher  vegetable  species  showed  no  power  to  spread  in 
plants  which  were  not  their  natural  hosts,  but  they  were  able  to  live 
at  inoculation-point  for  a  considerable  time. 

The  possible  objection,  already  alluded  to,  that  the  distribution  of 
the  bacteria,  which  was  noted  in  many  cases,  may  not  indicate  actual 
growth,  will  now  be  considered. 

The  observed  facts  are  these:  The  distribution  of  the  micro- 
organisms in  the  plant-axis,  as  determined  by  culture  experiments, 
always  took  place  in  an  ascending  direction.  This  distance  varied 
from  30-50  mm.  from  point  of  introduction,  but  in  no  case  were  bac- 
teria found  more  than  2-3  mm.  below  inoculation-point. 


Germ. 

Culture  from  Inoc. 
Point  showed  : 

Culture  made  from 
Tissue  taken. 

Bac.  luteus  in  Geranium  40  days. 

1850  colonies, 

10  mm.  above,  1764 

B.  fluorescens 

43 

4200 

5 

3850 

« 

<i 

« 

3 

below,    350 

B.  butvricus 

48 

104 

5 

above,      45 

" 

« 

«« 

10 

20 

B.  acidi  lactici 

35 

6500 

5 

4200 

«        « 

« 

« 

25 

2250 

«        « 

« 

«  « 

3 

below,  2000 

Of  course  the  numbers  given  above  do  not  represent  the  total 
number  of  bacteria  present,  owing  to  the  difficulty  of  preparing  tissue 
so  that  all  can  develop.  Besides  this  fact,  the  developing  colonies 
were  observed  to  be  usually  intracellular  and  not  in  the  spaces  of  the 
plant. 


Bacteria  in  their  Relation  to   Vegetable  Tissue.  9 

Now  let  us  consider  the  two  possible  theories,  besides  that  of  actual 
growth,  which  suggest  themselves. 

First,  that  of  diffusion.  For  this  a  fluid  substance  is  necessary 
that  is  continuous  throughout  the  plant.  As  the  cellulose  wall  and 
ectoplasm  of  the  vegetable  cell  act  as  an  effectual  filter  of  solid 
particles,  there  would  be  no  chance  for  direct  diffusion  from  cell 
to  cell.  The  inability  to  utilize  the  intercellular  spaces  for  this 
purpose  is  equally  evident,  for  these  are,  under  normal  conditions, 
filled  only  with  a  saturated  vapor,  and  not  fluid  substances,  and  there- 
fore unable  to  function  as  a  means  of  diffusion. 

If  simple  diffusion  were  operative,  then,  too,  we  would  expect  to 
find  the  bacteria  diffused  as  far  below  the  point  of  introduction  as 
above,  especially  as  gravity  would  aid  in  this  result.  This  is  con- 
trary to  the  experimental  facts. 

Now,  is  it  possible  to  explain  this  distribution  as  a  result  of  the 
transpiration  currents  in  the  stem? 

Whatever  may  be  the  ultimate  outcome  of  the  conflicting  theories 
regarding  the  locus  of  the  transpiration  stream,  it  rests  upon  the 
imbibitory  and  osmotic  powers  of  certain  vegetable  cells.  But  this 
stream  can  only  carry  substances  in  solution  through  these  vegeta- 
ble membranes,  and  therefore  could  not  function  as  a  transporter  of 
solid  bodies  like  bacteria.  This  was  demonstrated  by  cutting  the 
stem  of  a  thrifty  growing  plant  under  water,  and  then  transferring  it  to 
a  vessel  containing  a  nutrient  solution  to  which  a  dilute  culture  of  a 
germ  had  been  added.  It  was  found  that  in  the  exercise  of  the  ordi- 
nary processes  of  vegetation,  no  germs  were  detected  in  the  tissue  to 
any  considerable  distance  above  the  water  level.1 

Then,  too,  the  distribution  of  the  bacteria  in  different  tissues,  such 
as  the  cortical  and  pith  parenchyma,  as  well  as  the  fibro-vascular 
tissue,  could  hardly  be  explained  by  the  action  of  this  current. 

If  the  germs  were  mechanically  transported,  why  was  it  that  only 
certain  forms,  notably  saprophytes,  were  selected  ?  This  cannot  be 
accounted  for  on  the  ground  of  size  or  independent  motility  of  the 
organisms.  Some  forms,  such  as  B.  amylovorus,  were  able  to  exist  in 
large  numbers  at  inoculation-point  for  a  considerable  length  of  time, 

1  It  is  possible,  however,  that  a  slight  amount  of  fluid  may  be,  drawn  up  a  short 
distance  into  the  intercellular  spaces  and  vascular  lumina,  in  order  to  equalize  the 
negative  pressure  of  the  contained  air  which  is  found  often  in  these  cavities. 


10  H.  L.  Russell. 

but  did  not  seem  to  be  able  to  spread  throughout  plants  which  were 
not  its  natural  host. 

From  the  above  considerations  it  will  be  seen  that  there  is  no 
reasonable  ground  to  support  the  hypothesis  that  the  bacterial  distri- 
bution is  purely  physical. 

As  no  actual  openings  are  known  to  exist  in  the  walls  of  these 
cells  (if  we  except  the  very  minute  pores  through  which  the  plasmic 
strands  pass),  it  is  difficult  to  understand  how  the  bacteria  are  able 
thus  to  spread  from  cell  to  cell  unless  they  possess  the  power  of 
penetrating  the  cell  wall  by  the  action  of  vital  forces. 

This  ability  would  require  physiological  activity  which  could  not 
be  present  unless  they  were  able  to  exercise  their  ordinary  metabolic 
functions. 

This  penetrative  power,  among  certain  forms,  is  noteworthy  when 
we  compare  it  with  the  results  obtained  by  injecting  different  species 
into  the  animal  body. 

Von  Fodor 1  found  that  when  B.  termo,  B.  subtilis  and  B.  mega- 
terium  were  introduced  in  large  numbers  into  the  jugular  vein 
of  a  living  rabbit,  they  disappeared  completely  after  a  lapse  of  four 
hours. 

Wyssokowitsch 2  also  determined  that  the  time  necessary  to  com- 
pletely destroy  all  bacteria  contained  in  one  c.c.  of  culture  fluid, 
when  introduced  into  the  animal  body,  varied  from  15  min.  with 
Spir.  tyrogenum  to  7  hours  with  B.  acidi  lactici. 

The  rapid  disposal  of  these  forms  in  the  animal  body  is  correlated, 
as  Nuttall8  has  shown,  with  the  germicidal  property  of  the  blood- 
serum.  The  action  of  plant-tissue  upon  bacteria*  is  in  no  case  com- 
parable to  this,  and  would  suggest  that  the  plant  is  not  protected  in 
a  similar  manner.  This  point  will,  however,  be  considered  in  detail 
under  another  head. 

The  possible  explanation  for  the  upward  distribution  of  germs 
may  rest  upon  the  principle  that  growth  always  follows  the  lines  of 
least  resistance.  Not  only  are  food  materials  more  abundant  in  the 
rapidly  growing  apex,  but  the  thinner  and  less  developed  cellulose 
walls  offer  much  less  resistance  to  the  spread  of  the  germs  than  the 
more  matured  cell-membranes  of  the  older  tissue. 

1  Von  Fodor  :  Arch.  f.  Hyg.  IV  (1886),  129. 

2  Wyssokowitsch  :  Zeit.  f.  Hyg.  I  (1886),  3. 
3 Nuttall:  Zeit.  f.  Hyg.  IV  (1888),  353. 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  11 

Can  bacteria  penetrate  the  intact  healthy  tissue  of  the  plant  ? 
In  considering  this  question  we  may  disregard,  in  this  connection, 
those  cases  where  bacteria  have  gained  access  to  the  inner  tissues  by 
means  of  wounds,  and  have  been  able  to  live  there  for  a  certain  time. 
The  question  as  stated  above  is  of  practical  importance  in  pathology, 
for  if  micro-organisms  are  able  to  penetrate  the  intact  tissues,  this 
will  explain  the  way  in  which  infectious  material  may  be  distributed 
from  plant  to  plant. 

The  epidermal  tissues  of  the  plant  are  much  more  resistant  to 
external  influences  than  the  parenchymatous  elements.  This  is  due 
to  an  outer  layer  of  pure  cutin,  or  to  the  impregnation  of  the  cellu- 
lose walls  with  cutinized  layers.  This  resistant  sheath  is  replaced 
in  the  older  plant  by  a  thicker  and  more  resistant  corky  layer. 
These  protecting  tissues  are  not  perfectly  continuous  over  the 
exterior  of  the  plant,  but  are  pierced  by  numerous  small  openings, 
the  stomata,  which  afford  a  direct  communication  between  the  sur- 
rounding atmosphere  and  the  inner  cells  of  the  plant. 

What  is  now  to  prevent  the  entrance  of  micro-organisms  through 
these  minute  openings  in  the  outer  membrane? 

As  regards  fungi  we  know  that  some  species,  such  as  Cystopus 
candidus,  the  common  white  rust  of  Cruciferse,  do  gain  access  to 
the  inner  tissues,  first,  by  sending  their  germ-tubes  through  the 
stomata  into  the  intercellular  spaces.  As  these  spaces  are  devoid  of 
nutrient  material,  they  must  offer  but  poor  conditions  for  growth 
to  any  organism  that  is  not  able  to  extract  its  nutriment  from  the 
living  cell,  either  by  haustoria  or  by  penetrating  the  wall  and,  by 
means  of  ferment  action,  obtaining  access  to  the  protoplasmic 
materials  of  the  cell. 

With  bacteria  that  are  not  adapted  for  a  parasitic  existence  in  plant- 
tissue  it  is  not  yet  definitely  determined  whether  they  can  enter  by 
means  of  these  natural  openings.  I  was  unable  to  isolate  from  the 
tissue  of  different  plants  any  bacteria,  although  the  pots  and  their 
plants  were  watered  for  several  days  with  dilute  infusions  of  the 
different  germs.  The  results  I  obtained  are  not  at  all  in  harmony 
with  those  of  Lominsky,  who  found  that  wheat  could  infect  itself 
naturally  in  soil  seeded  with  different  species  of  bacteria.  Not  only 
was  he  able  to  isolate  from  the  roots  of  the  growing  plant  all  the 
species  which  he  added  to  the  soil,  but  he  found  them  also  in  the 


12  H.  L.  Russell. 

tissues  of  the  stem  and  leaves.  This  result  would  have  been  much 
more  convincing  had  he  used  larger  plants  than  wheat,  as  it  is  quite 
possible  that  the  bacteria  isolated  came  from  the  surface  rather  than 
the  inner  tissues  of  the  plant. 

Although  it  is  extremely  doubtful  if  those  micro-organisms 
whose  mode  of  nutrition  is  not  adapted  for  parasitical  existence  in 
vegetable  tissues,  can  enter  the  plant  without  the  intervention  of 
an  actual  wound,  it  is  much  more  probable  that  those  forms  naturally 
parasitic  on  plants  may  sometimes  succeed  in  thus  getting  a  foothold 
in  the  tissues. 

Bolley,1  in  his  work  on  surface  scab  of  potatoes,  tried  the  experi- 
ment of  infecting  sound,  healthy,  growing  tubers  with  liquid  cultures 
of  the  scab  bacilli.  The  growing  tubers,  after  thorough  cleansing, 
were  immersed  in  a  fluid  containing  an  infusion  of  the  scab  bacilli, 
and  the  glass  vessel  was  then  protected  from  outside  contamination. 
In  thirteen  days  the  tubers  so  treated  had  decayed,  while  a  control  test 
with  sterilized  water  showed  tubers  perfectly  sound  and  the  water 
clear.  He  reasons  from  this  that  the  bacteria  penetrated  the  growing 
lenticels  of  the  tuber.  He  also  repeated  the  experiment  by  saturating 
with  an  infusion  of  scab  bacilli  sterilized  soil  in  which  he  transplanted 
the  growing  tubers.  Control  tests,  watered  with  distilled  water  in- 
stead of  the  diluted  culture,  were  made,  and  he  found  that  infection 
took  place  when  the  bacteria  came  in  contact  with  the  healthy  tuber. 

With  the  pear-blight  germ  I  have  found  it  impossible  to  infect  even 
the  young  budding  leaves  and  stems  of  the  pear,  when  these  organs 
were  several  times  sprayed  with  a  culture  of  the  germ.  Susceptible 
as  well  as  refractory  varieties  failed  to  succumb  to  the  disease  when 
subjected  to  this  manner  of  infection.  Atomizing  the  flower  clusters, 
however,  usually  yields  positive  results,  according  to  Waite.  Here 
the  tissue  is  thinner  walled,  and  in  some  places,  as  the  nectary,  is 
destitute  of  cutin,  so  that  the  bacteria  have  less  difficulty  in  effect- 
ing an  entrance.  The  highly  nutritious  nectar  affords  them  an 
excellent  medium  for  growth,  and  here  they  are  able  to  thrive  until, 
as  Waite  has  suggested,  they  get  a  foothold.  It  is  quite  possible  that 
this  intermediate  stage  of  development  affords  an  opportunity  for 
the  accumulation  of  a  ferment  by  which  the  germs  are  able  to  more 
easily  penetrate  the  subjacent  tissue. 

1  Bolley :  Agric.  Science,  Vol.  IV,  250. 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  13 

Infection  experiments  with  Galloway's  oat-disease  succeeded 
usually  with  young  plants  when  they  were  simply  sprayed,  but  older 
and  more  developed  plants  failed  to  "take"  the  infection  this  way. 
This  may  possibly  indicate  that  the  stomata  do  not  function  as  a 
means  of  entrance,  as  the  older  plants  are  furnished  with  these 
structures  as  well  as  the  young  seedlings. 

Kellerman  thinks  that  Bac.  sorghi  is  able  to  penetrate  the  roots  of 
the  sorghum  cane,  as  the  young  roots  are  often  attacked  during  the 
disease,  the  infection  coming  apparently  from  the  soil.  Whether 
they  pierce  the  epidermis  itself,  or  enter  by  means  of  the  root-hairs, 
he  did  not  determine.  Beyerinck  found  that  through  the  root-hairs 
of  the  Leguminosse,  Bacillus  radicicola  was  able  to  enter  and  cause 
the  formation  of  tubercles. 

THE  ACTION  OF  BACTERIA  WITHIN  THE  TISSUES. 

How  are  bacteria  able  to  spread  throughout  the  tissues  of  the 
plant  ?  We  have  seen,  in  the  results  already  detailed,  that  with  certain 
forms,  mainly  saprophytic,  they  are  able  to  pass  from  cell  to  cell. 
That  they  do  this  in  plant-diseases  is  evidenced  by  the  lesions  that 
they  call  forth.  But  just  how  they  are  able  to  make  their  way  from 
cell  to  cell  is  by  no  means  so  evident.  In  the  light  of  our  present 
knowledge  concerning  the  transpiration  stream,  we  cannot  conceive 
of  this  current  being  utilized  as  a  bearer  of  solid  particles  unless  they 
have  an  inherent  power  of  penetrating  the  cell  wall.  We  do  not  find 
that  the  bacterial  plant-diseases  are  able  to  spread  their  infective 
material  throughout  the  plant  in  a  manner  comparable  to  a  septi- 
caemia, which  is  often  developed  in  animals.  This  they  would  be 
able  to  do  if  the  transpiration  current  could  function,  like  the  blood 
stream,  as  a  distributor  of  infection. 

It  is  possible  that  the  lumina  of  the  vascular  tissue  afford  the 
least  resistance  to  the  spread  of  infection,  yet,  so  far  as  .we  now 
know,  only  one  parasitic  species  has  adapted  itself  to  this  course. 
Wakker's  Bac.  hyacinthi  affects  primarily  the  xylem  tissue  of  the 
fibrovascular  bundle.  Not  only  does  it  occupy  the  cavity  of  these  air 
cells,  but  also  attacks  the  surrounding  walls,  chiefly  the  middle 
lamella,  which  it  soon  converts  into  a  disorganized  gummy  exudate, 
and  is  thus  able  to  spread  to  the  surrounding  tissue.1  Through  these 

1  Wakker:  Arch,  neer.,  T.  XXIII,  p.  6  (1888). 


14  H.  L.  Russell. 

elongated  vessels  it  is  able  to  spread  the  disease  quite  rapidly,  as 
has  been  demonstrated  by  artificial  infection  experiments. 

The  rapidity  with  which  the  pear-blight  germ  is  able  to  spread  its 
infective  material  through  a  susceptible  host  also  indicates  a  very 
rapid  movement  from  cell  to  cell.  This  is  especially  marked  in  the 
softer  succulent  tissue  of  the  youngest  twigs  and  in  the  blossoms. 
After  once  securing  an  entrance  to  the  rapidly  growing  tissues,  it 
sets  up  a  kind  of  fermentation  which  completely  destroys  many  of 
the  cells,  thus  forming  large  spaces  which  are  filled  with  the  gummy 
products  of  its  fermentative  activity.  Under  favorable  conditions, 
the  rapidity  with  which  the  blight  bacteria  spread  is  quite  surprising. 
The  following  laboratory  note  may  be  considered  fairly  indicative  of 
the  rate  of  distribution.  March  8,  a  Japan  seedling  was  infected  by 
puncture  of  the  young  stem.  March  13,  the  disease  had  manifested 
itself  by  a  local  blackening  of  the  tissue  in  the  neighborhood  of  the 
inoculation  point.  Two  days  later,  the  stem  showed  that  the 
disease  had  progressed  fully  six  inches  from  point  of  inoculation,  as 
indicated  by  blackened  appearance.  The  presence  of  bacteria  was 
also  demonstrated  microscopically  fully  an  inch  or  more  beyond 
this  blackened  tissue,  showing  that  the  spread  of  the  disease,  after 
having  once  established  itself,  was  quite  rapid. 

It  has  been  suggested  that  bacteria  are  able  to  pass  from  cell  to 
cell  through  minute  pores  in  the  walls.  Recent  investigations1  show 
that  the  direct  union  of  the  plasma  of  cell  to  cell  is  very  much  more 
widely  diffused  than  was  formerly  supposed,  and  that  all  the  living 
elements  of  the  whole  plant-structure  of  higher  plants  are  thus  united. 

These  plasmic  strand-connections  vary  in  diameter  from  0.05-1.0^, 
but  on  the  average  they  are  so  small  that  it  would  seem  hardly 
possible  that  they  coul^  be  utilized  by  the  bacteria  in  forcing  their 
way  from  cell  to  cell.  It  seems  much  more  probable  that  their 
progress  is  effected  by  ferment  activity.  In  the  case  of  the  pear- 
blight  germ  and  the  hyacinth-disease,  it  is  seen  that  the  healthy 
tissue  undergoes  a  decomposition  under  the  influence  of  the  bac- 
teria, resulting  in  the  production  of  a  gummy  substance,  and  in  the 
case  of  the  blight,  the  liberation  of  CO2. 

Bolley2  finds  the  germ  causing  the  surface  scab  in  the  potato  im- 

1  Kienitz-Gerlofi  :  Bot.  Zeit.  (1890),  XLIX,  1. 

2  Bolley :  Agric.  Science,  IV,  284. 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  15 

bedded  in  the  protoplasm  of  the  cell.  In  this  case  the  cell  mem- 
branes were  seen  to  be  actually  eroded  by  the  bacillus. 

A  similar  condition  is  found  with  B.  olese-tuberculosis  in  the 
olive,  and  B.  Veuillemini  in  the  tumors  of  Pinus  halapensis,  where 
actual  destruction  of  cell  walls  is  accomplished  under  the  influence 
of  the  germ.  It  is  not  at  all  improbable  that  those  species  which 
are  adapted  to  a  parasitic  existence  in  the  plant  organism  may  not 
possess  an  eroding  or  fermentative  ability,  which  would  enable  them 
to  break  down  the  resistant  cell  walls  which  impede  their  spread. 

But  how  do  we  find  it  with  those  forms  which  are  not  so 
thoroughly  adapted  to  this  kind  of  life  ?  It  is  much  more  difficult 
to  determine  the  distribution  in  these  cases  than  it  is  where  the  germ 
is  able  to  grow  luxuriantly.  With  the  results  which  were  obtained 
from  the  inoculation  of  those  micro-organisms  that  are  incapable  of 
producing  a  genuine  infection  in  plant-tissues,  it  has  been  shown  in 
several  cases  that  there  was  a  distinct  tendency  to  spread  throughout 
the  plant  to  a  certain  extent.  These  bacteria,  which  were  deter- 
mined at  greater  or  lesser  distances  from  the  inoculation  point, 
were  also  definitely  located  in  the  interior  of  the  cells.  This  condi- 
tion was  best  seen  with  cultures  of  B.  acidi  lactici,  but  was  also 
recognized  with  B.  luteus,  B.  pyocyaneus,  and  B.  fluorescens.  As 
has  already  been  said,  we  cannot  explain  their  presence  unless  they 
are  able  to  pass  through  the  cell  walls.  No  openings  of  any  kind 
could  be  determined,  and  the  only  remaining  possibility  that  sug- 
gests itself  is  that  they  have  the  power,  by  means  of  a  ferment 
excreted,  to  work  their  way  from  cell  to  cell  without  causing  a 
permanent  rupture.  This  we  know  to  be  the  case  with  certain 
Ustilaginese.  They  can  penetrate  the  cell  wall,  which,  after  the 
passage  of  the  hypha,  again  closes,  so  that  no  opening  is  apparent. 
With  as  small  a  structure  as  a  bacillus  this  process  is  also  con- 
ceivable. This  explanation,  however,  does  not  rest  upon  experi- 
mental proof  and  is  only  suggested  as  a  possible  hypothesis. 

RESISTANCE  AND  IMMUNITY  OF  PLANTS  TOWARD  BACTERIA. 

The  general  exemption  of  plants  from  bacterial  attack,  which  was 
referred  to  in  the  introduction  under  the  expression  "Immunity/' 
reveals,  upon  a  closer  consideration  of  the  question,  a  series  of 


16  H.  L.  Russell 

phenomena  of  a  complex  order.  In  the  appendix  to  this  paper  will 
be  found  a  complete  list  of  all  the  plant-diseases  which  are  now 
known  to  be  closely  associated  with  bacteria.  A  complete  com- 
pilation of  this  sort  has  not  previously  been  made  for  the  bacterial 
diseases  of  plants,  and  a  tabular  review  of  this  field  of  bacteriology 
was  thought  to  be  desirable.  Although  the  causal  relation  between 
a  specific  organism  and  a  plant-malady  has  not  in  every  case  been 
satisfactorily  and  thoroughly  demonstrated,  there  is  no  doubt  but 
that  most  of  the  plant-diseases  mentioned  may  be  rightfully  ascribed 
to  the  ravages  of  these  micro-parasites.  When  we  consider  how 
little  attention  has  been  paid  to  this  branch  of  phytopathology,  it 
is  no  wonder  that  our  information  on  this  subject  is  meager. 

The  list  of  diseases,  although  now  limited,  is  rapidly  and  con- 
stantly increasing,  so  that  we  may  freely  predict  that  with  a  more 
thorough  and  exhaustive  study  of  plant  pathology  from  a  bacterio- 
logical standpoint,  the  number  of  diseases  will  be  materially  aug- 
mented. Even  now  we  possess  sufficient  data  to  qualify  the 
assertion  that  plants  are  not  subject  to  diseases  of  a  bacterial  origin. 

A  closer  study  of  the  general  exemption  of  plant-structures  from 
the  attacks  of  micro-organisms  reveals  the  fact  that  the  phenomena 
heretofore  embraced  under  the  general  term  of  immunity,  are  not  of 
the  same  character  in  all  cases.  Different  phases  of  this  exemption 
seem  to  exist.  One  of  these  is  the  reaction  of  the  plant  toward 
micro-organisms  in  general.  The  other  is  the  ability  of  certain  plant- 
structures  to  withstand  the  inroads  of  a  particular  bacterial  parasite. 
Under  the  first  head,  the  micro-organism  is  unable  to  gain  a  foot- 
hold in  the  tissue  of  the  plant,  or,  having  once  gained  an  entrance 
accidentally,  it  is  unable  to  cope  successfully  with  the  repellant 
forces  resident  in  the  tissues.  There  is  no  susceptibility  on  the  part 
of  the  plant  toward  the  germ  in  question.  This  is  the  action  which 
living  tissue  exerts  in  general.  Where  this  action  is  overcome  and 
the  micro-organism  triumphs,  we  have  the  development  of  disease. 

Now,  the  ability  of  a  single  individual  to  withstand  the  attacks  of 
a  germ  capable  of  producing  a  disease  in  the  tissue  of  another  indi- 
vidual of  the  same  species,  is  evidently  a  different  action.  There 
is  a  certain  degree  of  susceptibility  on  the  part  of  the  plant  to  suc- 
cumb to  this  enemy,  as  is  evidenced  by  the  fact  that  when  the  con- 
ditions which  maintain  the  natural  balance  of  the  forces  inhibiting 
the  germ  are  disturbed,  the  germ  is  then  able  to  successfully  attack 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  17 

the  weakened  plant.      To  this  latter  class  of  phenomena  it  would 
seem  proper  to  limit  the  term  immunity. 

We  would  scarcely  consider  the  human  body  immune  from  the 
attacks  of  ordinary  saprophytes,  even  those  forms  which  are  normally 
found  in  the  oral  cavity.  Most  of  them  seem  to  possess  no  ability  to 
thrive  inside  of  the  animal  organism,  but  find  their  natural  condi- 
tions of  existence  in  the  dead  organic  material  which  is  always 
present  in  the  mouth.  Likewise,  it  would  seem  improper  to  say 
that  a  rose  is  immune  from  Bac.  tuberculosis  because  the  tubercle 
bacilli  do  not  find  in  the  tissues  of  the  plant  the  necessary  conditions 
for  their  development. 

While  the  bacterial  parasites  already  known  are  sufficient  to  indi- 
cate that  we  cannot  consider  the  vegetable  kingdom  as  wholly  free 
from  bacteria,  yet  we  must  admit  that  the  susceptibility  of  plants 
is  very  much  less  than  that  of  animals. 

In  considering,  then,  this  exemption  of  plants  from  the  attacks  of 
micro-organisms,  we  will  divide  the  phenomena  into  two  classes : 

First,  those  due  to  what  may  be  called  Resistance;  second,  those 
due  to  Immunity. 

Before  going  farther,  it  will  be  necessary  for  us  to  determine  the  limi- 
tations which  will  be  imposed  upon  the  meaning  of  these  two  terms. 

The  inherent  power  of  the  vegetable  organism  to  withstand  the 
action  of  bacteria  in  general  may  be  termed  Resistance.  This  resist- 
ance which  the  plant  offers  to  the  entrance  of  micro-organisms  may 
be  due  to  various  causes,  and  is  operative  throughout  the  whole  range 
of  plant  life.  It  is  the  normal  condition  of  the  plant,  and  is  closely 
correlated  with  the  conditions  of  nutrition,  for  when  the  natural  play 
of  these  forces  is  disturbed,  and  an  abnormal  state  of  affairs  super- 
venes, this  power  of  resistance  may  be  subject  to  greater  or  less  modi- 
fication. This  lowering  of  the  general  vitality  of  the  plant,  due 
possibly  to  a  number  of  causes,  is  usually  manifested  in  a  lessening  of 
the  powers  of  resistance  which  the  plant  seems  to  possess.  The  plant 
organism  becomes  then  more  susceptible  to  the  attacks  of  disease. 

This  state  of  affairs  must  not  be  confounded  with  a  condition 
which  affords  a  more  favorable  opportunity  for  the  development  of 
the  attacking  parasite.  The  one  concerns  itself  with  those  processes 
which  tend  to  lower  the  general  vitality,  and  thus  the  resistance  of 
the  plant ;  the  other  relates  only  to  those  conditions  which  give 


18  H.  L.  Rmsell 

increased  powers  of  development  to  the  attacking  organism.  It  is 
possible  that  the  same  set  of  causes  may  produce  this  double  effect, 
as,  for  instance,  such  meteorological  conditions  as  excessive  moisture, 
to  the  extent  that  it  not  only  interferes  with  the  normal  action  of 
the  vital  processes  of  the  plant,  but  gives  also  the  optimum  condi- 
tions for  the  development  of  the  parasite.  But  while  the  resultant 
of  these  forces  may  have  a  doubly  deleterious  action  on  the  plant,  it 
does  not  of  necessity  follow  that  this  should  be  the  case. 

It  will  have  been  seen  that  the  resistance  which  a  plant  offers 
toward  its  enemies  in  general  is  broad  and  wide-reaching  in  its  effects  ; 
not  so  with  immunity  in  regard  to  a  specific  disease.  The  one  is  a 
general  condition  of  normal,  healthy  vegetable  life ;  the  other,  the 
expression  of  a  restricted  group  of  vegetable  organisms  toward  the 
cause  of  a  specific  malady.  The  term  immunity  will  then  be  restricted 
to  those  plant-organisms  which  do  not  succumb  to  the  action  of  a 
germ  that  is  able  to  call  forth  a  genuine  infection  in  another  related 
species.  Thus  we  may  define  Immunity  in  plants  as  the  ability  of 
the  organism  to  repel  the  attacks  of  a  germ  which  produces  a  path- 
ological condition  in  a  closely  allied  form.  By  a  closely  allied  form, 
we  mean  a  species  or  variety  which  stands  in  close  taxonomic  affinity 
with  the  form  which  is  a  natural  host  for  the  germ  in  question. 
Now,  the  limit  of  this  immunity  must,  of  necessity,  be  a  somewhat 
variable  one.  Whether  the  term  should  be  restricted  in  its  applica- 
tion to  those  species  grouped  in  the  same  genus  or  subgenus,  or 
whether  it  should  embrace  the  limits  of  a  whole  family,  will  differ  in 
different  cases. 

Our  knowledge  of  the  ability  of  bacterial  germs  to  produce  in 
plants  a  diseased  condition  in  different  species  is  yet  somewhat 
limited,  but  the  observations  already  on  record  are  further  strength- 
ened by  analogous  cases  with  fungal  diseases. 

We  know  that  some  fungi  are  very  restricted  in  their  development, 
and  that  outside  of  a  single  host-plant  they  are  unable  to  call  forth 
any  diseased  condition,  even  under  the  most  favorable  opportunities. 
This  is  the  case  with  Fusicladium  pirinumj  which  causes  the  destruc- 
tive pear-scab  both  in  this  country  and  Europe.  Sorauer1  claims 
that  under  no  conditions,  even  during  the  seasons  which  are  most 
favorable  for  the  growth  of  the  fungus,  does  it  ever  exceed  the 

1  Sorauer :  Landw.  Versuchsstat.  XXVI,  327. 


Bacteria  in  their  Relation  to   Vegetable  Tissue.  19 

narrow  limits  which  form  apparently  its  fixed  boundaries.  On  the 
other  hand,  the  host-distribution  of  some  diseases  is  known  to  be 
dependent  largely  upon  certain  climatic  conditions.  During  years 
with  the  normal  amount  of  rainfall  or  seasons  of  drought,  the  fungi 
only  attack  the  ordinary  hosts  upon  which  it  is  a  natural  parasite, 
but  when  an  excessively  rainy  season  supervenes,  the  conditions 
being  then  much  more  favorable  for  the  development  of  the  parasite, 
the  fungus  is  reported  upon  many  new  hosts,  usually,  however, 
allied  species  within  generic  or  tribal  limits.  Swingle1  gives  an  inter- 
esting series  of  results  which  he  found  with  the  Peronosporese  on 
the  Euphorbise  in  Kansas,  corroborative  of  this  statement.  Here 
the  ordinary  boundaries  which  usually  limit  the  spread  of  the  fungus 
were  broken  over  during  those  years  that  were  particularly  favorable 
for  the  development  of  the  parasite,  and  the  same  parasitic  species 
was  often  found  on  entirely  new  hosts. 

These  two  extremes  indicate  the  impossibility  of  establishing  any 
hard  and  fast  line  for  the  limits  of  a  disease,  and,  consequently,  the 
limits  of  immunity  in  the  latter  example  would  be  much  wider  than 
in  the  former. 

So  far  as  is  at  present  known,  among  the  bacterial  plant-diseases 
we  have  no  malady  that  is  able,  either  in  a  state  of  nature  or  by  arti- 
ficial injection,  to  produce  a  pathological  condition  in  plants  belong- 
ing to  different  natural  families.  Such  a  condition  may  not  be 
impossible,  however,  and  further  research  may  give  us  examples 
which  have  a  wider  range  of  host-plants.  The  majority  of  them  are 
naturally  limited  in  their  distribution,  even  within  generic  and  often 
within  specific  boundaries. 

The  two  phases  to  which  this  exemption  of  plants  from  bacteria 
is  due,  immunity  and  resistance,  although  acting  distinctly  with 
reference  to  different  germs,  may  be  resident  even  in  the  same  plant 
organism.  A  plant  may  be  resistant  or  totally  insusceptible  toward 
an  ordinary  saprophyte  or  even  a  bacterial  parasite  whose  host-plant 
is  in  a  distant  family,  and  yet  may  or  may  not  possess  immunity 
from  another  species  of  bacteria  which  is  a  natural  parasite  upon  a 
closely  related  species. 

The  presentation  of  a  few  examples  of  what  is  meant  by  this  will 
suffice  to  illustrate  this  distinction  between  immunity  and  resistance. 

'Swingle  :  Kans.  Acad.  of  Science,  Vol.  VI,  1887-88. 


20  H.  L.  Russell. 

Reference  must  again  be  made  to  the  pear-blight  germ  (B.  amylo- 
vorus),  as  its  biology  is  the  most  thoroughly  investigated  of  any  of 
the  bacterial  plant-diseases.  So  far  as  is  known,  this  malady  is  con- 
fined strictly  to  the  Rosacea?,  and  almost  without  exception  to  the 
sub-order  Pomese.  It  has  been  reported  to  have  been  found  in  the 
young  fruit  of  the  Kelsey  plum1  (Primus  sp.),  where  it  was  traced  to 
the  sting  of  a  curculio,  when  the  eggs  were  deposited,  and  also  in  a 
new  disease  of  rasp-  and  blackberry.2  However,  this  last  exception 
has  not  yet  been  thoroughly  demonstrated.  Arthur  also  reports  that 
he  was  able  to  produce  a  slight  infection  in  the  succulent  shoots  of 
the  peach,  but  not  at  all  in  other  non-rosaceous  fruits,  as  mulberry 
and  grape.3  While  the  disease  afflicts  several  different  species  of 
Pomea3,  its  commonest  host  is  the  cultivated  pear.  The  early  history 
of  this  disease  shows  that  it  was  at  first  more  or  less  restricted  in  its 
development  on  this  species,  attacking  only  certain  varieties,  but  in 
the  wider  range  of  the  malady  in  later  years,  it  seems  to  have 
acquired  the  ability  of  successfully  attacking  other  varieties,  until 
now  we  know  of  no  variety  that  is  absolutely  immune,  in  the  state 
of  nature,  from  the  disease.  Although  not  wholly  immune,  many 
horticultural  strains  possess  immunity  in  a  partial  degree,  as  is  evi- 
denced by  the  fact  that  under  like  conditions  certain  varieties  yield 
much  more  readily  to  the  disease  than  others.  By  some  peculiarity 
in  the  structure  of  the  plant,  possibly  merely  mechanical  in  its 
nature,  one  variety  is  able  to  successfully  resist  the  attacks  of  the 
parasite  to  a  larger  extent,  and  thus  possesses  a  partial  natural 
immunity  from  the  disease. 

This  immunity  can  often  be  overcome,  however,  if  the  germs  are 
able  to  gain  access  to  the  tissues  in  some  manner,  as  by  wounds  from 
insect  stings,  etc. 

This  is  well  shown  by  the  following  greenhouse  experiment : 

Set  1.  Two  pear  trees  (Japan  seedlings4),  2  years  old,  were  inocu- 

1  Personal  communication  from  Mr.  M.  B.  Waite,  to  whom  I  am  indebted  for  a 
number  of  facts  bearing  on  this  topic. 

2Detmers:  Ohio  Bull.  Exp.  Stat.,  No.  6,  Oct.  1891. 

3Arthur:  N.  Y.  Ann.  Agri.  Exp.  Stat.,  1884,  362. 

4  This  stock,  lately  introduced  from  Japan,  is  in  great  favor  with  nurserymen  on 
account  of  its  vigorous  and  luxuriant  growth,  and  its  seeming  refractory  qualities, 
under  ordinary  conditions,  toward  the  blight.  Growers  have,  however,  not  had 
experience  with  it  long  enough  to  determine  whether  its  seeming  good  qualities  are 
of  a  permanent  nature  or  not. 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  21 

lated  with  B.  amylovor us,  sub-epidermally,  on  March  3.  March  12, 
the  blight  was  well  marked  as  a  blackened  patch  for  nearly  an  inch 
on  each  side  of  point  of  inoculation.  Period  of  incubation,  therefore, 
9  days. 

Set  2.  Two  2-year  old'  trees,  of  blight-proof  variety,  budded 
on  Japan  stock,  were  inoculated,  sub-epidermally,  March  17.  Evi- 
dence of  blighting  in  leaves  and  stems  readily  recognizable  on 
March  25.  Incubation  period,  8  days. 

Set  3.  2-year  old  budded  Clapp's  Favorite  (a  variety  readily  sus- 
ceptible to  the  disease  in  the  orchard)  was  inoculated  in  the  same 
manner,  March  3.  March  12,  diseased  condition  apparent,  although 
not  as  well  marked  as  in  Set  1.  Period  of  incubation,  9  days. 

From  this  set  of  experiments,  it  will  be  noted  that  those  varieties 
(Sets  1  and  2)  which  under  natural  conditions  are  known  to  be  much 
more  refractory  than  others  (3),  not  only  lost  their  partial  natural 
immunity  when  subjected  to  artificial  inoculation,  but  yielded  to  the 
disease  fully  as  quickly  as  did  the  variety  that  was  naturally  sus- 
ceptible. This  artificial  inoculation  is,  however,  a  much  severer  test 
than  they  receive  under  the  operation  of  ordinary  conditions  of 
cultivation,  but  it  shows  that  the  varying  degrees  of  susceptibility,  or, 
in  other  words,  immunity  can  be  overcome  under  certain  conditions. 

Waite  attempted  to  infect  two  different  species  of  Cratsegus  (C. 
oxyacantha  and  C.  tomentosa,  var.  parviflora)  by  atomizing  the 
flowers,  but  found  that  only  the  latter  succumbed  to  the  action  of  the 
germ.  Here  again  is  a  case  of  immunity  where  one  variety  is  exempt, 
under  certain  conditions,  from  the  disease.  The  immunity  in  this 
case  is,  however,  not  a  deep-seated  condition,  as  is  shown  by  the  suc- 
cessful infection  of  the  latter  variety  by  puncture  inoculation,  where 
the  bacteria  were  actually  introduced  into  the  tissues.  Other  species 
of  the  pomaceous  group  of  the  Rosacese  are  more  or  less  susceptible 
to  the  disease,  although  much  less  so  than  the  pear  and  apple.  The 
cultivated  species  of  this  fruit  family  seem  to  be  more  readily  suscep- 
tible than  many  of  the  wild  species.  Certain  species,  such  as  the 
Haw  (CrataBgus  spp.)  and  Shadbush  (Amelanchier  Canadensis),  are 
subject  to  the  disease  when  artificially  inoculated  with  the  germ. 

The  researches  of  Savastano1  on  the  tubercle  of  the  olive  tree  in 
Italy  also  aptly  illustrate  the  relation  of  immunity  and  resistance. 

1  Savastano :  Tuberculosi,  iperplasie,  e  tumori  dell'  olivo :  Ann.  R.  Scuola  Sup. 
d'Agric.,  Vol.  V,  1887.  ^T\ 

ur 


22  H.  L.  Russell. 

The  bacillus  causing  this  disease  produces  an  hypertrophy  of  the 
cambial  and  extra-cambial  tissue,  which  is,  however,  quite  local- 
ized. The  results  of  artificial  inoculation  into  young  olive  trees 
were  evident  in  25  days,  and  in  2  months  a  well-marked  swelling 
was  to  be  noted  at  seat  of  inoculation.  Savastano  was  not  able, 
however,  to  successfully  infect,  in  equal  degree,  all  varieties  of  this 
species,  but  found  a  varying  degree  of  susceptibility  in  different 
varieties.  When  the  B.  olese-tuberculosis  was  injected  into  other 
healthy  fruit-bearing  trees,  such  as  lemon,  bitter  orange,  pear,  apple, 
quince,  etc.,  no  trace  of  the  infection  could  be  noticed.  Here  is,  then, 
a  case  of  resistance  against  the  organism  even  though  it  was  a  para- 
sitic organism  on  other  forms  of  plant  life. 

He  also  infected  olive  trees  in  like  manner  with  several  other 
micro-organisms  which  he  found  associated  in  the  tuberculous 
growths  with  the  true  cause  of  the  disease,  but  in  no  case  was 
any  pathological  condition  brought  about,  showing  that  the  normal 
resistance  of  the  plant  was  able  to  overcome  the  accompanying  sap- 
rophytic  micro-organisms,  although  it  was  not  able  to  withstand  the 
attacks  of  the  parasite  in  all  cases. 

The  examples  already  cited  will  suffice  to  show  the  distinction 
made  between  immunity  and  the  normal  resistance  of  the  plant,  and 
also  that  immunity  is  a  varying  term  itself,  sometimes  applicable 
within  narrow  limits,  then  again  spreading  over  a  greater  variety  of 
species.  Not  only  are  the  limits  of  immunity  ill-defined  and  vary- 
ing, but  the  degree  of  immunity  also  varies  considerably.  This  is 
readily  recognized  in  horticulture,  when  we  say  that  one  variety  is 
more  susceptible  to  the  attacks  of  a  certain  disease  than  another. 
This  variation  of  the  susceptibility  of  different  varieties  indicates 
that  they  possess  an  immunity  to  a  greater  or  less  extent  from  the 
action  of  a  definite  specific  germ. 

We  might  consider,  also,  other  phases  of  immunity  which  present 
themselves  for  consideration,  but  a  mere  mention  of  these  will  be 
all  that  can  be  given  of  them  in  this  connection.  Thus  we  have  the 
local  immunity,  which  certain  tissues  enjoy  against  the  attacks  of 
micro-parasites  as  they  increase  in  age  and  consequently  become 
better  developed  and  more  resistant.  This  rests  on  a  purely  physical 
basis,  and  the  importance  of  it  will  be  considered  later  more  in  detail. 
This  local  immunity  of  certain  tissues  is  strongly  reinforced,  also, 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  23 

by  a  consideration  of  the  phenomena  connected  with  certain  fungal 
diseases,  as  in  the  case  of  Cystopus  Candidas,  which,  according  to 
De  Bary,  can  only  successfully  infect  the  host-plant  when  it  enters 
the  young  cotyledons  of  the  plant.  Hypoderma  macrosporon  is 
only  able  to  gain  entrance  into  the  pine  through  the  young  pine 
cones. 

This  law  usually  holds  in  connection  with  the  bacterial  plant- 
diseases.  Most  of  them  are  more  virulent  in  their  course  when  they 
attack  young  and  undeveloped  hosts,  and  not  a  few  are  apparently 
inhibited  after  the  tissues  have  reached  a  certain  stage  of  maturity, 
as  in  the  case  of  the  oat-disease  of  Galloway  and  the  pear-blight. 

CAUSES  OF  IMMUNITY  AND  RESISTANCE. 

Having  cited  special  cases  illustrative  of  resistance  and  immunity, 
we  may  now  turn  to  the  consideration  of  the  possible  factors  which 
are  able  to  cause  these  conditions.  To  this  difficult  problem  we  can- 
not hope  as  yet  to  give  any  definite  and  conclusive  answer.  The  rapid 
progress  which  has  been  made  in  this  department  of  animal  biology 
within  the  past  five  years  indicates  how  vast  and  complicated  the 
question  is  in  all  its  bearings.  The  accumulating  data  which  have 
already  been  collected  have,  however,  contributed  much  to  a  better 
conception  of  the  problem  of  immunity,  and  lead  us  to  believe  that 
any  experimental  consideration  of  this  subject  in  relation  to  plants, 
even  though  negative  in  its  results,  is  not  entirely  without  value. 

The  attempt  has  been  made  in  the  previous  pages  to  show  that 
there  are  two  factors  at  work  in  the  struggle  of  the  plant  with  its 
parasitic  enemies.  We  shall  not,  however,  attempt  to  prove  that  the 
phenomena  which  are  considered  as  resistance  and  immunity  are 
brought  about  through  the  action  of  separate  and  distinct  forces.  It 
is  possible,  and  quite  probable, -that  the  conditions  which  produce 
one  factor  may  also  be  the  cause  of  the  other.  For  instance,  in 
animal  biology,  Wyssokowitsch  determined  that  certain  saprophytes, 
as  well  as  some  parasites,  disappeared  completely  when  introduced  into 
the  blood  of  a  living  rabbit.  Nuttall  determined  that  the  cause  which 
destroyed  saprophy tic  as  well  as  pathogenic  organisms  was  the  same, 
namely,  the  germicidal  property  of  the  body  fluids.  Although  the 
result  was  brought  about  through  the  operation  of  the  same  cause, 


24  H.  L.  Russell. 

we  would  not  consider  these  two  cases  similar.  The  one  is  simply 
the  normal  resistance  which  the  animal  offers  to  an  organism  which 
has  no  power  under  any  circumstances  to  produce  a  diseased  condi- 
tion in  its  body.  The  other  is  a  case  of  immunity  to  a  certain 
degree  against  the  pathogenic  organism. 

We  cannot,  however,  compare  the  phenomena  of  animal  immunity 
too  closely  with  that  of  plants,  as  we  find  that  the  causes  which  tend 
to  produce  this  state  are  unlike  in  the  two  kingdoms.  A  much 
closer  similarity  exists  between  the  immunity  of  plants  from  bacteria 
and  from  fungi.  Not  only  are  the  phenomena  presented  quite 
homologous  in  character,  but  the  causes  which  are  operative  are  no 
doubt  more  or  less  closely  related. 

It  will  be  hardly  possible  to  classify  the  causes  which  may  tend 
to  produce  the  resistance  and  immunity  of  the  plant  from  its  bacterial 
foes  in  any  satisfactory  and  complete  manner.  A  tentative  classifi- 
cation, however,  may  be  suggested  along  the  lines  of  physical  and 
chemical  action  ;  including  under  physical  sources  all  those  mechan- 
ical contrivances,  such  as  epidermal  covering,  cutinization  of  tissues, 
and  the  secondary  thickening  and  lignification  of  cell  membranes, 
which  enable  the  plant  to  ward  off  injurious  external  forces.  Under 
chemical  sources  we  would  class,  not  only  the  reaction  of  the  tissues 
and  the  nutritive  conditions,  but  the  resistant  action  due  to  the  living 
protoplasm  itself. 

That  one  of  the  possible  causes  of  the  partial  immunity  which 
some  plants  exercise  toward  parasitic  forms  is  dependent  largely 
upon  the  mechanical  obstructions  which  the  plant  offers  to  the 
entrance  of  the  germ,  is  seen  in  the  examples  of  immunity  which 
have  already  been  mentioned. 

Certain  strains  of  the  common  pear,  under  ordinary  conditions  of 
cultivation,  are  quite  refractory  toward  the  blight  when  subjected  to 
natural  infection  which  takes  place  in  the  blossom  through  insect 
visitation,  but  these  varieties  when  artificially  inoculated  sub-epider- 
mally  with  bacteria  yield  readily  to  the  disease.  This  can  scarcely 
be  accounted  for  on  any  other  ground  than  that  the  blight  bacteria 
are  unable  to  gain  a  foothold  on  account  of  some  peculiarity  of  the 
external  plant  membranes.  This  may  be  so  slight  that  one  cannot 
detect  any  histological  difference  in  the  exterior  cells,  yet  one  variety 
will  be  considerably  more  refractory  under  natural  conditions  than 
the  other. 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  25 

Arthur1  has  drawn  attention  to  this  point  and  suggests  that  these 
differing  degrees  of  susceptibility  are  due  to  physical  causes. 

Not  only  has  mechanical  exclusion,  as  a  cause  of  immunity,  been 
shown  in  the  pear-blight  disease,  but  other  bacterial  diseases,  as  well, 
illustrate  the  operation  of  this  cause.  In  his  inoculation  experi- 
ments upon  "  La  Jaune  des  Jacinths,"  Wakker2  infected,  besides  a 
number  of  susceptible  varieties  of  the  hyacinth,  one  variety  (Norma) 
which  was  regarded  under  natural  conditions  as  immune  from  the 
disease.  This  he  found  succumbed  as  readily  to  the  malady  as  the 
naturally  susceptible  varieties  when  the  infective  material  was 
introduced  into  the  leaf  of  the  plant,  showing  that  the  natural  immu- 
nity of  the  variety  was  dependent  upon  its  epidermal  tissue. 

These  two  cases,  cited  above,  are  examples  where  immunity  of  the 
plant  toward  a  specific  parasite  is  dependent  upon  a  physical  means 
of  exclusion,  but  the  same  cause  is  also  operative  in  regard  to  the 
general  resistance  of  the  plant  against  all  forms  of  germs.  Under 
ordinary  circumstances  we  do  not  find  that  saprophytic  organisms, 
even  decomposition  bacteria,  are  able  to  enter  the  normal,  healthy, 
intact  plant  structure,  yet  we  have  shown  in  the  preceding  pages 
that  these  germs  when  they  once  get  a  foothold  into  the  plant  tissue 
are  able  to  survive  for  a  long  time,  and  where  the  vitality  of  the 
host  is  much  reduced  may  even  cause  a  disorganization  of  tissue. 

If  the  thin  cutinized  layers  of  epidermal  cells  afford  such  an  effectual 
barrier  to  the  entrance  of  micro-organisms,  the  more  resistant  corky 
layers  of  the  mature  plant  will  be  even  more  efficacious  in  excluding 
germ  life  in  general.  This  is  demonstrated  by  the  complete  inability 
of  most  bacterial  diseases8  to  penetrate  the  resistant  tissues  of  the  bark. 
These  act  as  an  efficient  barrier  against  the  entrance  of  any  organisms, 
except  through  the  natural  openings  (lenticels)  and  wounds. 

Although  the  cuticular  and  cortical  layers  of  the  plant  function 
as  the  chief  hindrances  to  the  entrance  of  germs,  fungal  as  well  as 
bacterial,  the  fully  developed  walls  of  the  inner  cells  also  inhibit 
the  spread  of  pathogenic  forms.  The  young  fruit  of  the  pear 
cannot  be  successfully  infected  after  it  has  reached  a  certain  size,  as 

'Arthur :  Proc.  Phil.  Ac.  Nat.  Sc.  1886,  p.  340. 

2  Wakker:  Arch,  norland,  d.  Sc.  ex.,  T.  XXIII,  p.  18. 

3Savastano  thinks  that  B.  olese-tuberculosis  must  make  its  way  through  the  bark 
tissue  in  order  to  reach  the  succulent  cambium  where  it  thrives.  But  this  idea  is 
conjectural  and  is  not  based  upon  experimental  proof. 


26  H.  L.  Russell. 

the  tissues  become  so  mature  that  the  germ  is  not  able  to  pass 
from  cell  to  cell.  It  is  also  particularly  prominent  in  the  blighting 
stem,  where  the  disease  is  usually  confined  to  the  youngest,  most 
succulent  tissue.  This  is  characteristic  of  bacterial  plant-diseases  in 
general,  that  the  most  pronounced  lesions  are  always  found  in  tissue 
which  has  not  yet  lost  its  power  of  growth.1 

We  turn  now  to  consider  the  chemical  sources  of  protection  which 
the  plant  may  possess  against  its  enemies.  First  of  all  we  have  the 
chemical  reaction  of  the  plant-tissues.  As  was  noted  in  the  intro- 
duction, it  is  to  this  source  that  most  authors  ascribe  the  general 
freedom  of  plants  from  bacteria.  This  was  before  it  was  thoroughly 
proven  that  vegetable  structures  were  affected  to  any  extent  by  bac- 
terial diseases,  and  was  probably  based  upon  the  then  prevailing 
idea  that  bacteria  required  alkaline  and  fungi  acid  substrata  for 
their  development.  So  many  exceptions  to  this  law  are  now  known 
that  this  statement  has  lost  much  of  its  original  force.  Most  of  those 
forms  which  we  know  to  be  able  to  cause  bacterial  plant-maladies 
are  usually  more  or  less  indifferent  to  the  reaction  of  the  medium, 
growing  in  either  weakly  acid  or  alkaline  nutrient  media.  Arthur 
succeeded  in  raising  B.  amylovorus  in  2  per  cent  malic-acid  bouillon. 

The  experiments  already  detailed  indicate  that  saprophytes,  and 
even  some  animal  pathogenic  forms,  are  not  destroyed  by  the  plant 
juices  either  within  or  outside  of  the  plant.  Forms  like  B.  prodi- 
giosus,  B.  lac.  aerogenes,  B.  megaterium,  B.  coli  commune,  Kiel 
water-bacillus  and  blue  pus  germ  grew  in  the  expressed  plant  juices  of 
various  kinds  and  produced  a  considerable  turbidity  in  24-48  hours. 

It  would  seem,  then,  that  the  importance  of  this  factor  as  the 
prime  cause  of  immunity  and  resistance  has  been  considerably  over- 
estimated. Very  much  more  stress  is  to  be  laid  upon  the  mechan- 
ical barriers  which  the  plant  possesses  against  the  entrance  of  germs, 
as  well  as  the  activity  of  the  living  protoplasm. 

The  nutritive  conditions  offered  by  the  plant  may  also  be  con- 
sidered in  this  connection.  While  the  dead  tissues  of  many  plants 

1  The  observation  which  Prillieux  noted  in  the  case  of  B.  Vuillemini,  which  causes 
the  tumors  in  the  old  wood  of  the  Aleppo  pine  (Pinus  halapensis),  is  only  apparently 
contradictory.  The  fact  that  a  local  hypertrophy  of  tissue  was  produced  by  means 
of  the  bacterial  stimulus  showed  that  the  tissues  were  yet  in  a  secondary  meri- 
stematic  condition. 

2Zopf:  DiePilze,  S.  173. 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  27 

afford  a  tolerably  good  substratum  for  the  development  of  many 
species  of  bacteria,  and  thus  show  that  the  tissues  are  not  wanting 
in  the  necessary  nutritive  materials,  the  conditions  are  different  in 
the  struggle  between  the  disease  germ  and  the  living  plant.  Unless 
the  germ  is  able  to  gain  access  to  the  inner  tissues  by  means  of  acci- 
dental lesions,  it  must  force  its  way  through  the  epidermal  cell 
walls,  or  the  cell  membranes  of  the  interior  tissue,  either  directly 
from  the  outside,  or  after  having  first  gained  an  entrance  through 
the  stomata  into  the  intercellular  spaces.  In  either  case  it  has  no 
supply  of  nutrient  material  with  which  to  carry  on  its  metabolic 
activity,  and  is  therefore  unable  to  gain  a  foothold  from  which  to 
develop. 

If  the  bacteria  could  increase  in  sufficient  numbers  on  the  surface 
of  the  plant  they  might  be  able  to  penetrate  the  tissues  more  easily. 
That  B.  amylovorus  is  in  this  way  able  to  gain  access  to  the  tender 
tissues  of  the  receptacle  of  the  pear-flower  is  extremely  probable. 
The  sugary  secretions  which  are  poured  out  by  the  nectariferous 
glands  in  the  flower  induce  insect  visitation,  and  afford  the  best 
possible  medium  for  the  growth  of  the  bacilli  which  are  brought  to 
it  in  the  sticky  exudate  which  adheres  to  the  insect.  Thus  the 
bacteria  have  a  fertile  soil  prepared  for  their  further  development, 
and  are  able  to  multiply  with  ease.  Having  thus  secured  such  a 
coigne  of  vantage,  they  are  able  to  penetrate  the  non-cutinized  tissues 
beneath,  and  thus  gain  entrance  to  the  inner  parts  of  the  plant. 

Do  plant  juices  possess  germicidal  properties  f 

Recent  experiments  in  animal  pathology  have  demonstrated  that 
the  blood  of  many  animals  possesses  the  property  of  destroying 
bacteria  to  a  limited  extent,  either  when  brought  directly  in  contact 
with  it  in  the  body  of  the  animal,  or  after  it  had  been  aseptically 
removed.  This  bactericidal  power  of  the  blood  enables  the  animal  to 
destroy,  not  only  the  saprophytic  forms  with  which  it  comes  in  con- 
tact, but  also  a  certain  number  of  even  malignant  bacteria,  which 
otherwise  would  be  able  to  multiply  in  the  body  and  finally  produce 
death.  This  line  of  investigation,  so  fruitful  of  results  in  immunity 
in  the  animal  kingdom,  suggested  a  series  of  experiments  as  to 
whether  a  corresponding  condition  might  not  exist  in  plant  life  as 
well. 

Although  we  have  in  plant-tissue  nothing  homologous  to  the  circu- 
latory fluids  of  the  animal  body,  it  might  be  conceivable  that  the 


28  H.  L. 

plant  fluids  were  endowed  with  a  gerraicidal  property  for  the  pro- 
tection of  the  plant.  If  the  plant  possessed  such  a  peculiarity,  an 
examination  of  the  cell  sap,  with  this  point  in  view,  ought  to  indicate 
its  presence.  The  first  difficulty  to  be  met  with,  however,  is  to 
secure  the  cell  sap  free  from  solid  elements  and  in  an  aseptic  con- 
dition. This  can  be  accomplished  without  serious  difficulty  in  the 
case  of  the  blood,  but  as  there  is  no  special  channel  for  the  move- 
ment of  the  plant  fluids,  the  problem  here  is  not  so  easily  solved. 

In  a  foregoing  set  of  experiments,  in  which  different  species  of 
bacteria  were  artificially  introduced  into  the  plant-tissues,  it  was  found 
in  a  number  of  cases,  particularly  with  saprophy  tic  forms,  that  they 
had  multiplied  to  a  limited  extent.  This  at  first  might  indicate  that 
the  plant-juices  had  no  germ-destroying  power.  Such  a  conclusion 
need  not  necessarily  follow.  It  has  already  been  found  that  the 
germicidal  action  of  the  body  fluids  towards  certain  organisms  has 
a  definite  limit,  and  that  when  too  many  germs  are  brought  in  con- 
tact with  it  its  capacity  for  destroying  the  bacteria  is  overcome, 
and  the  germs  are  able  to  increase  and  call  forth  a  pathological  con- 
dition in  the  body.  That  such  might  have  been  the  case  in  the 
above  experiments  was  possible,  as  large  numbers  of  bacteria  were 
introduced  into  the  plant. 

To  determine  this,  experiments  were  carried  out  on  plant-tissues 
to  determine  if  the  plant-juices  possessed  any  germicidal  properties. 
Heating  could  not  be  resorted  to  as  a  means  of  sterilization,  as  this 
would  affect  any  property  analogous  to  the  germ-killing  peculiarity 
of  the  blood,  so  the  only  recourse  was  to  obtain  the  juices  aseptically. 
Trituration  in  a  small  sterilized  mortar  was  first  attempted,  but  this 
method  was  regarded  as  unsatisfactory  on  account  of  the  cellular 
detritus  present.  Expression  of  the  juice  was  then  tried  by  com- 
pression. A  small  screw  press,  capable  of  being  sterilized,  was  used 
for  this  purpose,  and  as  the  fluid  escaped  through  the  minute  open- 
ings in  the  bottom  it  was  caught  in  a  sterilized  receiver  and  pipetted 
into  small  culture  bulbs  as  before.  By  this  process  the  plant-juice 
was  secured  perfectly  free  from  solid  particles.  Into  this  culture 
fluid  a  number  of  germs  were  inoculated,  as  determined  by  NuttallV 
device  for  accurate  quantitative  work,  and  at  varying  intervals  of 
time  the  germ-contents  of  the  bulbs  were  determined.  In  each  case 

'Nuttall:  Bull.  J.  H.  H.  No.  13,  May-June,  1891. 


Bacteria  in  their  Relation  to   Vegetable  Tissue. 


29 


about  5-7  cc.  of  the  expressed  juice  was  used.  The  quantitative 
results,  indicated  in  the  following  table,  show  the  influence  of  the 
plant  j  uices  upon  the  growth  of  different  species  of  micro-organisms. 


Name  of  Germ. 

No.  used  as 
"Seed." 

Period  of 
Incubation. 

No.  at  end  of 
Experiment. 

Plant  Juice 
used. 

Kiel  water-bacillus  .  . 

859 
26 

2  hrs.  40  min. 
24   " 

6700 
8420 

Canna. 

« 

Bac.  lactis  aerogenes. 
B.  coli  commune  

26 
26 

46 

5    " 
24   " 

24   " 

90 
7200 

12  480 

n 
it 

1  1 

B  meffaterium 

14 

1  hr   45  min 

25 

ti 

14 
14 

20 

7   " 
10  hrs.  30  min. 

4   it 

215 
3060 

35 

« 
«  i 

it 

20 

105 
105 

24  " 

4   " 
24   " 

4600 
160 
32,000 

<  i 
n 
it 

Most  of  the  species  which  were  used  in  the  above  experiment  are 
those  which  showed  a  marked  increase  when  in  the  plant-tissues  for 
a  considerable  period  of  time.  This  table,  however,  indicates  that 
the  increase  began  immediately  upon  the  introduction  of  even  small 
numbers  into  the  cell  sap,  showing  that  this  fluid  possessed  no  bac- 
tericidal properties. 

The  attempt  to  test  the  action  of  cell  sap  was  also  tried  in  another 
way.  However,  this  method  did  not  allow  of  accurate  quantitative 
determination,  although  the  other  conditions  were  more  nearly 
normal.  It  was  based  upon  the  action  of  root  pressure  in  the  plant. 
Thrifty  young  plants  with  good-sized  stems,  like  the  Lima  bean  or 
geranium,  were  selected,  and  after  having  washed  the  stems  with  a 
disinfecting  solution,  they  were  cut  off  with  a  sterile  knife  about  an 
inch  from  the  ground.  The  stump  of  the  plant  was  then  quickly 
covered  with  a  short  sterile  test-tube,  which  made  a  moist  chamber 
that  prevented  evaporation.  The  pot  was  then  set  in  a  warm  place 
to  induce  copious  root-action,  and  in  12  to  24  hours  a  large  drop  of 
cell  sap  had  exuded  from  the  cut  end  of  the  stem.  This  clear  fluid 
was  then  inoculated  with  a  few  germs  from  a  fresh  culture,  to  be 
tested,  and  after  a  varying  length  of  time  their  relative  number 
determined  as  nearly  as  possible. 


30  H.  L.  Russell. 

A  marked  increase  with  B.  megaterium,  B.  butyricus,  B.  coli 
commune  and  B.  pyocyaneus  was  noted,  while  Strept.  pyogenes  in 
five  days  was  killed.  As  the  death  of  the  bacteria  inoculated  did 
not  occur  at  once,  but  was  gradual,  it  was  no  doubt  due  to  unfav- 
orable nutritive  conditions  rather  than  any  germicidal  effect  of  the 
cell  fluids. 

The  cell  sap  usually  possesses  a  distinct  acid  reaction,  and  would,, 
no  doubt,  inhibit  the  growth  or  kill  out  by  malnutrition  those  forms 
susceptible  to  acid  reaction.  Some  plant-juices  afford  a  much  better 
nutritive  medium  than  others,  such  as  the  sugar-cane  or  the  saccha- 
rine varieties  of  sorghum,  or  the  sap  of  such  trees  as  Acer  sacchari- 
num.  Sternberg1  has  recommended  the  milk  in  green  cocoanuts  as  a 
nutritive  medium  for  even  animal  pathogenic  organisms.  This  i& 
really  the  elaborated  cell  sap  of  the  embryo-sac. 

In  the  animal  body  we  find  that  a  bactericidal  property  is  not 
only  resident  in  the  blood  plasma  and  tissue  juices,  but  is  also  found 
in  various  secretions  and  excretions  which  are  formed  in  the  animal 
organism. 

Thus  the  sputum  of  a  healthy  individual  is  known  to  have  an 
anti-bacterial  effect  on  anthrax,2  while  the  germicidal  properties  of 
fresh  milk 8  and  urine 4  are  quite  considerable. 

Although  we  have  been  unable  to  detect  any  analogous  property 
in  the  cell  sap  of  the  plant,  we  know  that  the  plant  is  able  in  many 
cases  to  protect  itself  by  means  of  its  secretions.  Thus  conifers  are 
protected  from  disease  in  many  cases  by  the  copious  flow  of  turpen- 
tine, which  forms  an  effectual  barrier  against  the  entrance  of  fungi  as 
well  as  bacteria.5  The  ethereal  oils  which  are  found  so  widely 
distributed  throughout  the  plant  kingdom  are  known  to  possess 
the  ability  of  hindering,  and  in  many  cases  actually  destroying, 
germs  when  brought  in  contact  with  them.6  In  all  probability  they 
function  in  a  similar  way  in  the  plant,  although  many  parasites  may 
have  adapted  themselves  to  this  condition. 

1  Sternberg :  Phil.  Med.  News,  1890,  p.  262. 
2Nuttall:  Boylston  Essay,  Harvard,  1888. 

3  Fokker:  Zeit.  f.  Hyg.,  IX  (1890),  41. 

4  Lehmann:  Cent.  f.  Bakt.  VII  (1890),  457. 
6  Hartig:  Die  Baumkrankheiten,  S.  139,  166. 

6Cadeac  et  Meunier  :  Ann.  de  PInst.  Past.  1889,  317.  Freudenreich  :  Ann.  de 
Microg.,  1889. 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  31 

Besides  the  possible  sources  of  immunity  and  resistance  which  we 
have  already  considered,  we  have  the  action  of  the  living  plasma  of 
the  plant.  Concerning  the  exact  nature  of  this  force  we  have  but 
little  positive  knowledge,  although  it  is  probably  chemical  in  its 
action.  We  know  that  the  plant  endowed  with  vital  activity  is  more 
resistant  toward  outside  influences  than  the  same  dead  structure;  also, 
that  protoplasm  which  is  in  an  active  state  is  much  less  subject  to 
the  attacks  of  disease  than  quiescent  or  inactive  protoplasm.  This 
has  been  demonstrated  in  the  case  of  a  number  of  tree-destroying 
fungi  that  are  only  able  to  overcome  the  tissue  cells  during  the  winter 
season  of  rest.1  Anything  that  tends  to  impair  the  normal  exercise 
of  the  vital  functions  of  the  protoplasm  predisposes  the  plant  to  the 
attack  of  outside  organisms.  It  is  quite  unlikely  that  this  so-called 
lowering  of  the  general  vitality  affects  to  any  considerable  extent  the 
physical  means  of  resistance.  It  is  much  more  probable  that  it  is 
the  repelling  ability  of  the  living  protoplasm  that  is  weakened,  and 
thus  less  resistance  is  offered  to  disease.  To  this  action  Marshall 
Ward  attributes  a  large  share  of  the  resistance  of  the  plant  against  its 
parasitic  foes. 

Speaking  of  fungi,  he  says,  so  long  as  the  protoplasm  can  over- 
come, by  respiratory  oxidation  or  otherwise,  the  small  amounts  of 
poison  generated  by  the  parasite,  the  hypha  does  not  pass,  but  when 
the  poison  exceeds  this  power  of  repulsion,  then  it  effects  an  entrance 
into  the  cell.2 

In  here  presenting  the  sources  which  seem  to  be  operative  in  the 
production  of  the  resistance  and  immunity  of  plant-tissues,  examples 
have  also  been  given  illustrative  of  this  condition  with  fungi  as  well 
as  bacteria.  While  the  conditions  necessary  for  the  best  develop- 
ment of  these  two  classes  of  vegetable  life  are  often  different,  there 
can  be  but  little  question  that  the  same  means  of  protection  which 
the  plant  possesses,  operates  in  many  cases  against  the  one  quite  as 
effectually  as  against  the  other.  The  refractoriness  of  higher  plants 
against  bacteria  has  many  more  points  in  common  with  the  same 
phenomena  against  fungi,  than  it  has  with  the  action  of  the  animal 
body  against  bacterial  life. 

1  Hartig:  Die  Baumkrankheiten,  S.  87,  112,  33  u.  A. 

2  H.  Marshall  Ward  :  Journ.  Roy.  Soc.,  1890,  213. 


32  H.  L.  Russell. 


CONCLUSIONS. 

For  sake  of  convenience,  a  short  review  of  the  points  which  have 
been  developed  in  the  preceding  pages  will  now  be  made. 

1.  The  increasing  importance  of  the  bacterial  portion  of  phyto- 
pathology necessitates  a  more  thorough  investigation  of  the  influence 
of  bacterial  life  in  general  upon  plant-tissue  than  has  heretofore  been 
considered  necessary. 

2.  The  artificial  inoculation  of  higher  plants  with  different  micro- 
organisms (not  known  to  be  pathogenic  for  plants)  reveals  the  fact, 
contrary  to  the  usually  accepted  idea,  that  quite  a  goodly  number  of 
different  species  are  able  to  withstand  the  action  of  the  living  plant 
organism  for  a  not  inconsiderable  length  of  time. 

3a.  Of  the  species  which  are  able  to  live  in  plant-tissues  for  a  con- 
siderable period  of  time,  those  which  are  ordinarily  adapted  to  a 
saprophytic  method  of  existence  are  particularly  prominent.  Not 
all  saprophytes,  however,  possessed  this  power,  but  in  certain  forms, 
as  B.  fluorescens,  B.  acid,  lact.,  B.  butyricus,  etc.,  it  was  a  marked 
feature. 

36.  Among  those  forms  which  are  facultative  parasites  upon  the 
animal  body,  but  few  were  found  that  seemed  to  be  able  to  live 
in  plant-tissue.  With  the  exception  of  B.  pyocyaneus  and  the 
Schweineseuche  bacillus,  they  gradually  decreased  in  numbers  and 
finally  died. 

3c.  The  inoculation  of  plants,  not  taxonomically  related  to  the 
natural  hosts  of  bacterial  plant  parasites,  with  species  of  micro- 
organisms naturally  parasitic  on  vegetable  tissue,  showed  that  while 
the  bacteria  were  unable  to  spread,  they  could  survive  at  the  inocu- 
lation point  in  large  numbers. 

4.  Not  only  were  numbers  of  different  species  of  bacteria  able  to 
live  in  the  plant  from  40  to  80  days  or  more,  but  many  of  them 
(mostly  saprophytes)  were  able  to  spread  throughout  the  tissue  of  the 
plant  to  a  limited  extent  (20  to  50  mm.  or  more). 

5.  The  local  distribution  always  took  place  in  an  upward  direc- 
tion, and  the  bacteria  were  found  to  be  generally  intracellular  instead 
of  intercellular. 

6.  According  to  the  present  views  of  physiologists  regarding  the 
transpiration  stream,  it  does  not  seem  possible  that  this  current  can 


Bacteria  in  their  Relation  to    Vegetable  Tissue.  33 

account  for  the  distribution  of  bacteria  in  the  tissue.  It  seems  to  be 
correlated  much  more  closely  with  the  actual  growth  of  the  micro- 
organisms. 

7.  The  facts  already  determined  relative  to  the  ability  of  sapro- 
phytes to  thrive  in  plant-tissues  throw  some  light  on  the  question 
of  the   normal  presence   of  bacteria   in    healthy  plants.     A  large 
number  of  cultures  made  from  the  inner  tissue  of  healthy  plant  stems 
revealed  no  bacteria,  but  where  stems  were  wounded,  even  by  a 
needle-prick,  the  bacteria  on  the  surface  were  able  to  enter  and  live 
for  a  long  time.     Thus  it  is  possible  that  bacteria  may  enter  through 
lesions  so  small  as  to  escape  notice,  or  they  might  even  live  in  the 
tissue  after  the  wound  had  healed  over. 

8.  With  bacteria,  not  adapted  for  growth  in  plants,  I  have  been 
unable  to  prove  that  they  could  enter  the  plant  where  the  epidermal 
tissue  was  known  to  be  intact.     In  the  case  of  parasitic  species  on 
plants,  they  sometimes  effect  an  entrance  into  tissues  without  the 
intervention  of  wounds  of  any  sort. 

9.  The  actual  method  by  which  saprophytes  are  able  to  spread  in 
plant  tissues  has  not  been  satisfactorily  determined,  but  it  seems  that 
the  cellulose  wall  undergoes  a  change  that  renders  it  permeable  to 
the  bacteria.     Those  forms  causing  a  pathological  condition  in  the 
plant  spread,  in   many  cases,  by  means  of  the  fermentative  and 
destructive  power  they  possess. 

10.  The  phenomena,  heretofore  regarded  as  immunity  of  plants 
from  micro-organisms,  present  two  phases  so  distinct  in  their  action 
that  it  seems  proper  to  separate  them  to  a  certain  degree.     The 
exemption  of  plants  from  bacteria  in  general  is  due  to  what  may  be 
termed  the  resistance  of  the  plant,  while  the  more  restricted  term, 
immunity,  is  reserved  for  the  ability  of  a  certain  group  of  plants  to 
be  refractory  toward  a  disease  germ  that  is  able  to  cause  a  patho- 
logical condition  in  closely  allied  forms  of  plant  life.     No  hard  and 
fast  limits  can  be  drawn  for  the  immunity  of  plants,  as  this  condition 
varies  in  each  disease.     The  causes  which  bring  about  this  ability  of 
the  plant  to  repel  not  only  bacteria  in  general,  but  those  toward 
which  it  is  somewhat  susceptible,  are  various. 

In  the  case  of  immunity,  physical  causes,  such  as  the  epidermal 
and  cortical  resistant  tissues,  matured  and  thickened  cell  walls  of  the 
inner  tissue,  exclusion  by  gummy  exudates,  etc.,  are  the  leading 


34  H.  L.  Russell 

factors.  The  exemption  of  plants  from  bacterial  diseases,  however, 
does  not  rest  upon  any  single  factor  but  upon  the  interaction  of 
various  causes. 

Added  to  this  mechanical  source  of  immunity  are  the  chemical 
reaction  of  the  juices,  the  unfavorable  conditions  of  nutrition,  the 
action  of  the  living  protoplasm,  etc.,  all  of  which  exercise  an  unfa- 
vorable or  inhibitory  effect  on  bacterial  life. 

The  whole  question  of  immunity  of  plants  from  bacteria  is  much 
more  closely  related  to  the  same  question  as  regards  fungi  than  it  is 
to  the  subject  of  immunity  as  seen  in  the  animal  kingdom.  Vege- 
table cell  juices,  aside  from  their  acid  reaction,  are  entirely  powerless 
against  bacteria,  and  do  not  possess  any  germicidal  properties  like  the 
blood-serum  of  animals. 

BIBLIOGRAPHY. 

A.  On  the  normal  presence  of  bacteria  in  healthy  tissue: 

1.  Bernheim  :  Munch,  med.  Wochen.,  1888,  s.  743. 

2.  Buchner:  Munch,  med.  Wochen.,  1888,  No.  52. 

3.  de  Vestea:  Ann.  de  PInst.  Pasteur,  1888,  670. 

4.  Fazio:  Revista  inter.  d'Igiene,  1890.     (Abs. :  Cent.  f.  Bakt. 

VII,  798.) 

5.  Fernbach :  Ann.  Past.,  1888,  567. 

6.  Groucher  et  Deschamps:  Arch.  Med.  Exp.,  1889,  53. 

7.  Galippe:  C.  R.  Soc.  Biol.,  1887,  No.  25. 

8.  Laurent:  Bull.  PAcad.  roy.  de  Belg.,  t.  X,  38. 

9.  Laurent:  Bull.  PAcad.  roy.  de  Belg.,  t.  XIX  (1890),  468. 

10.  Lehmann:  Munch,  med.  Wochen.,  1889,  No.  7. 

11.  Ralph:  Trans.  Royal  Soc.  Victoria,  Vol.  XX,  1884. 

12.  Van  Tieghem:  Bull.  Soc.  Bot.de  France,  1884,  XXXI,  283. 

B.  On  the  artificial  inoculation  of  plants  with  bacteria,  non-parasitic  in 

vegetable  tissue : 

1.  Lominsky  :    On  the  parasitism  of  some  pathogenic  microbes 

for  animals  in  living  plants.    Wratsch,  1890,  No.  6.    (Ref. 
Cent.  f.  Bakt.  VIII,  325.) 

2.  Savastano :   Tuberculosi  delP  olivo :  Ann.  R.  Scuola.  Sup. 

d'Agric.  in  Portici,  Vol.  V,  1887. 


Bacteria  in  their  Relation  to   Vegetable  Tissue.  35 

APPENDIX  GIVING  A  LIST  OF  THE  BACTERIAL  PLANT  DISEASES, 
WITH  BRIEF  KESUME  OF  THEIR  PRINCIPAL  CHARACTERISTICS. 

The  preparation  of  a  complete  abstract  of  the  bacterial  diseases  of 
plants  at  present  is  attended  with  some  difficulty.  Besides  the  num- 
ber of  well  authenticated  and  confirmed  observations  upon  this  class 
of  diseases,  there  are  quite  a  number  of  maladies  which  have  been  as 
yet  incompletely  worked  out.  The  disease  has  been  experimentally 
reproduced  only  by  inoculation  of  diseased  tissue,  not  by  infection 
from  a  pure  culture  of  the  germ.  The  classic  canons  of  Koch,  which 
are  regarded  as  essential  in  the  elucidation  of  the  etiology  of  an 
animal  disease,  are,  however,  just  as  applicable  in  the  investigation 
of  plant  maladies,  and  we  can  consider  no  disease  as  sufficiently 
proven  to  be  of  bacterial  origin  until  the  germ  has  first  been  isolated, 
and  then  successful  inoculation  experiments  made  with  the  pure 
culture  of  the  organism. 

The  literature  embracing  this  branch  of  phytopathology  is  largely 
American,  but  it  is  widely  scattered,  and  it  was  thought  that  a  brief 
resume  of  the  bacterial  plant-diseases  known  to  date  would  be  of 
value.  So  far  as  I  am  aware,  this  has  not  yet  been  attempted  in  any 
complete  degree.  Gomes'  Crittogamia  Agraria  (Naples,  1891)  and 
Ludwig's  Lehrbuch  der  Niederen  Kryptogamen  (Stuttgart,  1892) 
are  the  only  works  from  a  European  source  that  attempt  to  deal  in 
any  satisfactory  way  with  the  bacterial  plant-diseases,  and  even  these 
include  only  a  part  of  the  diseases  already  known. 

Tables  I  and  II  give  a  list  of  those  diseases  which  have  been  traced 
to  a  bacterial  origin  and  where  the  disease  is  claimed  to  have  been 
experimentally  produced  by  inoculation  of  pure  cultures.  Table  III 
gives  a  provisional  list  of  diseases  possibly  of  bacterial  origin,  but 
the  etiology  of  each  malady  has  not  yet  been  traced  to  a  specific 
microbe,  and  consequently  cannot  be  regarded  as  thoroughly  proven. 

The  number  of  plant  maladies  caused  by  bacteria  might  have  been 
considerably  increased  if  all  the  cases  on  record  of  the  presence  of 
bacteria  in  diseased  tissue  had  been  added.  This,  however,  does  not 
signify  that  the  bacteria  bear  any  etiological  relation  to  the  disease, 
and  it  is  possible  that  in  many  of  these  cases  they  are  present  only 
as  decomposition-organisms  in  dead  or  dying  tissue.  A  considerable 
number,  however,  of  these  have  been  added,  as  it  has  been  suggested 
that  it  might  be  useful  to  collect  the  data  on  this  subject,  imperfect 
or  otherwise,  which  at  present  are  so ,  widely  scattered  in  various 
publications. 


TABLE  I. — BACTERIAL  PLANT  DISEASES. 


SPECIFIC  NAME  OF 
GERM. 


Bac.  amylovorus 
(Burrill)    De  Toni. 


Bac.  sorghi, 
Burrill. 


NAME  OF 
DISEASE. 


Pear  blight. 
Fire  blight. 


Sorghum 
blight. 


HOST  PLANTS  AFFECTED  BY  NATURAL  AND 
ARTIFICIAL  INFECTION. 


Pear  (Pyrus  communis). 

Apple  (P.  malus). 

Anier.  mountain  ash  (P.  Americana). 

Crab-apple  (P.  sinensis). 

Quince  (Cydonia  vulgaris). 

English  haw  (Cratsegus  oxyacantha). 

"      (C.  tomentosa,  var.  parviflora). 
Shadbush  (Amelanchier  Canadensis). 
Red  raspberry1  (Turner  and  Marlboro  var.) 
Blackberry  (var.  Snyder). 
Kelsey  plum  (Prunus  sp. ) 


llu  horizontal  column  refers  to  Detmer's  work. 
Actual  inoculations  in  this  case  not  made. 


Sorghum  vulgare. 

#)  saccharine  var. 

b)  non     " 
S.  halapense? 


(broom  corn). 


ORGANS  OF  PLANT 
AFFECTED. 


Flower  clusters,  young 
fruit,  more  succulent 
woody  tissue  and  foliage. 


1  Base  of  stem  and 
branches. 


Leaf-sheaths  and  leaves, 
roots. 


Bac.  Zese, 
Burrill. 
(Bac.  secales.) 


Corn  blight. 


Zea  mays. 


Roots,  stem  (lower  inter- 
nodes),  leaves  and  sheath, 
fruit. 


Bac.  hyacinthi, 
Wakker. 


Yellows  of 
hyacinths. 


Hyacinthus  orientalis. 


Xylem  portion  of  fibro- 
vascular  bundle  in  bulbs 
and  leaves ;  parenchyma 
in  leaves. 


Bac.  hyacinthi 
septicus. 
Heinz. 


Hyacinth  rot. 


Hyacinthus  sp,  sp.  Allium  Cepa. 


B.  oleae-tuberculosis, 

Savastano. 
(B.  oleas)  Trev. 


Tuberculosis. 

(Rogna) 

Italy. 

(Maladie  de 
la  loupe) 

France. 


Olea  Europea. 


Leaves,  flower  clusters, 
and  bulbs. 


Cambium  and  bast  of  old 
as  well  as  young  wood. 


MODE  OP 
NATURAL  IN- 
FECTION. 


IMMUNE  AND  RESISTANT  SPP.  AS 

TESTED  BY  ARTIFICIAL 

INOCULATION. 


GENERAL  REMARKS. 


BIBLIOGRAPHY. 


Insects  during 
fertilization  of 
flower,  punc- 
ture by  insect 
stings,  bites, 
etc. 


Cydonia  Japonica,  atomizing  flowers. 

Peach,  nearly  immune.     (Arthur.) 

Grape, 

Mulberry, 

Corn, 

Potatoes, 

Bean, 

Onion, 

Wheat  and  oats. 


Natural  immunity  of  diff.  species  of 
pear  family  lost  when  subjected  to 
artificial  inoculation. 


A  general  infection  usually 
affecting  the  more  succulent 
parts  of  tree,  recognized  by 
the  blackened  or  burnt  ap- 
pearance (hence  name  fire 
blight)  of  part  affected,  also 
by  gummy  exudate. 


Burrill :  3d  111.  Rep.  Agri. 
1890.  Amer.  Nat.  VII 
(1883),  319.  Trans.  111. 
Hort.  Soc.  1877,  1878.  111. 
Indus.  Univ.  Rep.  1882. 

Arthur :  4th,  5th  and  6th 
N.  Y.  Agri.  Exp.  Rep. 
Proc.  Acad.  Sc.  Phil.  1886. 
Amer.  Nat.  XIX  (1885), 
1181.  Proc.  Amer.  Ass. 
Adv.  Sc.  1885.  Bot.  Gaz- 
ette X,  343. 

Waite :  Unpublished  work 
of  U.  S.  Ag.  Dept.,  Div.  of 
Veg.  Path. 

1  Detmers  :  Ohio  Bull.  No. 
6,  1891. 


Stomata  and 
roots. 


Zea  mays. 

Triticum  vulgare. 

Sorghum  vulgare  (some  varieties). 

Some  varieties  of  sugar  sorghum 

(Kellerman  and  Swingle). 


Disease  affects  principally 
leaves  and  their  sheaths,  also 
the  roots.  Parts  affected 
show  a  crimson  red  patch, 
usually  circumscribed,  not 
causing  a  rupture  on  the  sur- 
face. Cell  contents  degen- 
erate, walls  turn  red. 


Burrill:  8th  Rept.  Soc. 
Prom.  Ag.  Sc.  1887.  Micro- 
scope, Nov.  1887. 

Kellerman  and  Swingle : 
Kans.  Rep.  1887  and  1888. 
Bull.  No.  5,  Dec.  1888. 

See  J.  of  M.  V.  195  for 
discussion  of  a  sorghum  dis- 
ease by  Comes. 


Artificial  in- 
oculation suc- 
ceeded without 
puncture. 


Closely  allied  to  sorghum 
germ  in  appearance  and  by 
its  pathological  changes  in 
tissue.  Dark  brown  discolor- 
ations  on  leaves.  Where  root 
is  affected  whole  plant  suffers 
in  loss  of  nutrition. 


Burrill:  3d. 111. Rep.  1890. 
Am.  Assoc.  Ad.  Sc.  1889. 
Soc.  Prom.  Ag.  Sc.  1889. 
111.  Bull.  No.  6, 1889. 

Duncanson :  Nebr.  Acad. 
Sc.  II. 


All  double  red  varieties  and  some  other 
double  varieties  immune  under  nat- 
ural conditions,  but  lose  immunity 
when  artificially  infected. 


Disease  restricted  in  its 
spread  throughout  tissue, 
causing    a    degeneration    of 
primary  cell  wall  and  cell 
contents,  forming  a  gummy 
exudate,  yellow  in  color. 


Wakker :  Bot.  Cent.  XIV 
(1883),  315.  Arch,  neer- 
land.  XXIII  (1888),  1. 


Disease  pro- 
duced arti- 
ficially from 
pure  cultures. 


From  description  of  disease 
and  of  germ,  this  disease 
appears  to  be  distinct  from 
Wakker's  malady.  Decom- 
position of  affected  parts  with 
formation  of  foul-smelling 


Heinz :  Cent,  f .  Bakt.  1889, 
Bd.  IV,  S.  535. 


Growing  point 
(?)    Savastano. 
Stomata  and 
lenticels 
(Prillieux.) 


Peach,  plum,  apricot,  grape,  fig,  pear, 
apple,  bitter  orange,  lemon,  rose,  and 
several  coniferous  trees. 


Bacteria  cause  destruction  of 
tissue  and  formation  of  spaces 
in  tissue.  This  induces  sec- 
ondary local  growth  and 
causes  an  internal  hypertro- 
phy in  bark  which  finally 
produces  local  death  of  tissue. 


Savastano:  Ann.  d.  R. 
Scuola  Sup.  d'Agric.  in  Por- 
tici,  Vol.  V,  fasc.  IV,  1887. 

Cavara :   Monograph, 
1889. 

Prillieux :  Monograph, 

1890.  C.  R.  Acad.  CVII 
249. 

Pierce:    Journ.  of    Myc. 

1891,  140. 


38 


H.  L.  Russell 


TABLE  II. — BACTERIAL  PLANT  DISEASES. 


SPECIFIC  NAME  OP 
GERM. 

NAME  OF 
DISEASE. 

• 
HOST  PLANTS  AFFECTED  BY  NATURAL  AND 
ARTIFICIAL  INFECTION. 

ORGANS  OF  PLANT 
AFFECTED. 

B.  Veuillemini, 
Trev. 
(B.  pini,  Vuill.) 

Tumors  of 
Aleppo  pine. 

Pinus  halapensis. 

Mature  wood,  especially 
cambium  and  phloem. 

Bacillus  avenae, 
Galloway. 

Blight  on  oats. 

Avena  sativa. 

Young  plants  (all  parts). 

Micrococcus  of  car- 
nation blight 
Arthur. 

Carnation 
blight. 

Carnation  pinks,  other  varieties  of  pinks. 

Leaves. 

Bacillus  of  surface 
scab  of  potato 
Bolley. 

Superficial 
potato  scab. 

Solanum  tuberosum. 

Tubers  (only  young), 
locally  in  stems,  young 
sprouts  and  leaves. 

Bact.  of  wet  rot 
Burrill. 

Wet  rot  of 

potato. 

Potato  (S.  tuberosum). 

Tubers,  possibly  leaves 
and  culms  also. 

Bac.  of  wet  rot 
Kramer. 

Nassfaule. 
(Wet  rot.) 

Potato. 

Tubers. 

Bacillus  of  beet-root 
disease. 
Arthur  and  Golden. 

Sugar  beet- 
root disease. 

Beta  vulgaris  (saccharine  varieties). 

Parenchyma  of  roots  and 
leaves,  also  fibre  -vascular 
tissue  to  less  degree. 

Bacteria  in  thdr  Relation  to  Vegetable  Tissue. 


39 


MODE  OF 
NATURAL  IN- 
FECTION. 

IMMUNE  AND  RESISTANT  SPECIES  AS 

TESTED  BY  ARTIFICIAL 

INOCULATION. 

GENERAL  REMARKS. 

BIBLIOGRAPHY. 

Insect  wounds 
(Vuillemin). 
Stomata  and 
lenticels. 
(Prillieux). 

Closely  allied  to  B.  olese- 
tuberc.  Bacteria  cause  a 
degeneration  and  partial  de- 
struction of  tissue.  This  irri- 
tation causes  hypertrophy  of 
cambial  and  bast  tissue  which 
produces  an  excrescence. 

Prillieux  :  Monograph, 
1890.    Ref.:  Zeit.  f.  Pflan- 
zenkrank.  I,  161. 
Comes  :  Crittogamia 
Agraria. 
Vuillemin:    C.  R.  Acad. 
CVII  (1888). 
Bot.  Zeit.  1889,  686. 

Stomata  (?). 
Artificial  in- 
fection suc- 
ceeds with 
simple 
spraying. 

Triticum  vulgare, 
Zea  mays, 
Sorghum  vulgare, 
Hordeum  vulgare, 
Diff.  spp.  grasses. 

Young  plants  (6-12  inches 
high)  are  particularly  sus-, 
ceptible  ;  affects  first  the  tips 
of  lower  leaves,  gradually 
extending  throughout  the 
whole  plant. 

Galloway:     J.   of  M.  VI 
(1890).    Bot.  Gazette,  XV, 
228.      Amer.   Assoc.   Aug. 
1890. 

Artificial  in- 
fection suc- 
cessful upon 
external  ap- 
plication. 

Characteristics  of  disease  ill- 
defined,   gradual    dying    of 
leaves.  Bacteria  found  abund- 
antly in  transparent  spots  on 
leaves. 

Arthur:  A.  A.  A.  S.  Aug. 
1890.     Soc.  Prom.  Ag.  Sc. 
Ind.  Exp.  St.  Bull.  1890. 

Lenticels. 

Aerial  organs  quite  immune. 

A  disease  favored  by  exces- 
sive moisture,  producing  a 
proliferation  of  lenticels,  al- 
lowing easier  access  of  bac- 
teria which  produce  a  super- 
ficial "scab." 

Bolley:  Ag.  Sc.  IV,  Nos. 
9  and  10.      A.   A.   A.   S. 
(1890),  334-5. 

A  soft,  wet  rot  emitting  an 
offensive  odor—  germ,  motile, 
0.7x1.  —  1.5  n,  non-liquefy- 
ing bacillus.  Proof  of  bacte- 
rial cause  not  yet  conclusive. 

Burrill  :  Proc.  Soc.  Prom. 
Ag.  Sc.  1890,  p.  21. 

Lenticels  or 
wounds. 

A  liquefying  butyric  acid 
producing  bacillus.  Infec- 
tion experiments  made  only 
with  ripened  tubers. 

Kramer:  Oest.  land.  Cent. 
I,  11.     Ref.:  Cent.  f.  Bak. 
X,  164. 

Unknown. 

Characters  of  disease  in  roots 
not  well  defined  ;  leaves 
puffed  out  in  intervening 
areas.  Disease  diminishes 
the  sugar  contents  of  roots 
to  a  considerable  extent. 

Arthur  and  Golden  : 
Ind.   Bull.    No.    39,    Apr. 
1892.     Abst.  in  Exp.  Stat. 
Rec.  Ill,  No.  12. 

40 


H.  L.  Russell. 


TABLE  III. — PLANT  DISEASES,  PROBABLY  OF  BACTERIAL  ORIGIN. 


NAME  OF 
DISEASE. 

HOST  PLANTS 
AFFECTED. 

CHARACTERISTICS  OF  THE 
DISEASE. 

RESULTS  OF  ARTIFICIAL 
INOCULATION. 

BIBLIOGRAPHY. 

Geranium 
blight, 
Bac.  caulivor- 
us.Pr.&Delx. 

Pelargonium,  diff. 
spp.  cult. 
Geranium,  cult. 
Potatoes  (stems). 

A  complete  disorganiza- 
tion of  tissue  of   young 
stems,    especially    "cut- 
tings "  of  Geranium,  which 
manifests  itself  by  a  black- 
ened shriveled  appearance, 
often  extending  to  leaves. 

Successful  inoculation 
made  with  diseased  tissue 
of  Geranium  in  healthy 
tissue  of  same  plant  ;  also 
infection  of  Geranium 
from  potato  stems  and  vice 
versa.     (Prill,  et  Delx.) 

Galloway, 
Journ.  of  Myc.  VI, 
114. 
Prillieux    and    Dela- 
croix, 
C.  R.   Acad.   CXI, 
208. 

Cucumber  rot. 
Tomato  blight. 

Cucurbitaceous 
plants  like  melons, 
cucumbers,  squash, 
also  tomatoes  and 
tubers  of  potatoes. 

Disease  marked  by  a  very 
rapid  decay  of  the  stem 
and  leaves  as  well  as  fruit. 
In  case  of  potatoes,  the 
aerial  parts  show  a  blight- 
ed appearance,  while  the 
tubers  present  a  watery, 
decayed  mass. 

Healthy  plant  stems,  es- 
pecially young  succulent 
ones,  as  well  as  fruit  (to- 
mato)   were    thoroughly 
rotted  by  inoculation  of 
diseased    tissue  in  short 
time  (6-24  hours). 
*  See  note  below. 

Halsted, 
Amer.  Ass.  Ad.  Sc. 
1891.   Bull.  No.  19, 
Miss.     Exp.     Stat. 
Jan.  1892. 

Root  rot  of 
vegetables. 

Salsify,  egg  plant, 
sweet  potato,  Irish 
potato,  onion,  and 
apple. 

A  slimy  and  very  offen- 
sive decomposition  of  root 
crops  beginning  at  lower 
end  and  working  its  way 
to  the  crown  of  plant. 

Disease  produced  by  trans- 
fer of  diseased  tissue  to 
healthy  plants. 

Halsted, 
Garden  and  Forest, 
Nov.  26,  '90.     llth 
N.J.Agr.  Exp.  Stat. 
351. 

Cabbage  rot. 

Cabbage,  turnips. 

General  rot  of   cabbage 
heads. 

Positive  results  obtained 
by  inoculating  diseased 
tissue  into  healthy  plants. 

Gorman, 
Amer.   Assoc.  Coll. 
and  Exp.  Stat.  1891. 

"Sereh" 
disease. 

Sugar  cane  (Java 
and  Sumatra). 

Diseased  plant  has  short 
internodes,  small  leaves, 
poorly  developed  root  sys- 
tem and  a  general  appear- 
ance   of    an    insufficient 
water  supply.  This  is  due 
to  the  stoppage  of  ves- 
sels by  a  gummy  slime, 
thought  to  be  the  product 
of  bacterial  growth. 

Two  distinct  spp.  ob- 
served by  Janse,  B.  sac- 
chari  and  B.  glagae,  but 
no  infection  experiments 
made  with  pure  cultures. 
Causal  relation  of  bac- 
teria to  disease  is  not  yet 
thoroughly  proven. 

Janse  : 
Ref  .  in  Cent,  f  .  Bakt. 
XI,  641. 
Kruger  : 
Ber.  d.  Vers.   Stat. 
f.  Zucker,  1890. 
Benecke. 

Certain  "Gum" 
diseases. 
Bact.  gummis, 
Comes. 

Various  plants, 
such  as  figs,  grapes, 
mulberry,  to- 
matoes, potatoes, 
cabbage,  beets, 
carrots,  etc. 

Disease  seems    to   affect 
starch-bearing  cells  and 
vessels.      The   starch    is 
decomposed  and  there  is 
formed    a    gummy    sub- 
stance that  stops  up  the 
vessels.     Bacteria  found 
in     abundance    in    this 
gummy  exudate. 

In  all  probability  there 
are  several  distinct  dis- 
eases under  this  head. 
Comes  and  Sorauer  both 
claim  to  have  isolated 
bacteria  that  were  able 
to  set  up  this  disturbance 
in  fresh,  healthy  tissue. 

Sorauer  : 
Zts.  f.  Pflanzkrank. 
11,280. 
Comes: 
Crittogam.  Agraria. 

*  Cross  inoculations,  made  between  tomato,  potato  and  melon  from  virus  of  one  species  on  to  the  other,  showed 

that  the  rot  was  common  to  all. 


Bacteria  in  their  Relation  to    Vegetable  Tissw. 
TABLE  III. — Continued. 


41 


NAME  OF 
DISEASE. 

HOST  PLANTS 
AFFECTED. 

CHARACTERISTICS  OF  THE 
DISEASE. 

RESULTS  OF  ARTIFICIAL 
INOCULATION. 

BIBLIOGRAPHY. 

Celery  blight. 

Celery. 

Affects  leaves  and  their 
stems,  diseased  tissue  pre- 
senting a  watery  appear- 
ance. 

Germ  observed  in  tissue, 
isolated  and  cultivated. 
When  introduced  into 
plant  caused  rapid  decay. 

Halsted: 
N.  J.  Bull.  Q.  Apr. 
21,  '92. 

White  slimy 
Flux, 
Leuconostoc 
Lagerheimii, 
Ludw. 

Oaks,  poplars, 
ash,  willows. 

Subcortical  tissue. 

Contagious  disease  dis- 
seminated by  insects  and 
caused  by  the  symbiosis 
of  this  germ  with  an  en- 
domyces  and  a  yeast 
fungus. 

Ludwig  : 
Lehr.  d.  nied.  Krypt. 
1891. 

Brown  slimy 
Flux,  Microc. 
dendroporthos, 
Ludw. 

Fruit  trees,  shade 
trees,  like  elms, 
poplars  and 
birches. 

Affects  wood  and  bark  of 
trees.  Disease  marked 
by  the  exudation  of  a 
yellowish  brown  slime 
from  wood  layers  which 
ultimately  destroys  the 
bark  of  tree. 

Seems  to  be  caused  by  a 
germ  which  Ludwig  has 
named  Mic.  dendropor- 
thos. Associated  with 
this  is  usually  Torula 
moniliodes,  corda. 

Ludwig  : 
Lehr.  d.  nied.  Krypt. 
'91.     Also,  Cent.  f. 
Bakt.  1891,  10. 

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